Signs Of Dissolution Research Articles

Water column barium sulfate dissolution and shielding by organic matter aggregates: Implications for the pelagic barite proxy

Pelagic barite (BaSO4) and related proxies are useful tools for reconstructing the marine carbon cycle. The factors controlling pelagic barite dissolution in the ocean water column are poorly understood, which adds uncertainty to Ba-based reconstructions. Here, we conducted static laboratory incubations to test the sensitivity of barium sulfate dissolution rate to a range of commonly occurring seawater pH, salinity, and temperature conditions. We observed relatively rapid dissolution rates ranging from 1.7 ± 0.4 to 3.4 ± 0.8 pg BaSO4 day−1 for these experiments, and we did not observe statistically significant differences in the rate of dissolution with varying pH, salinity, or temperature. The slowest dissolution rate observed in these experiments suggests that an average barium sulfate crystal would survive in the ocean water column just 6.2 ± 0.3 days. We estimate that an average isolated pelagic barite crystal would take 67 years to sink down through the water column, so our experiments imply that solitary pelagic barite crystals do not survive this transit. We conducted an additional experiment on a roller table to assess the impact of organic matter aggregates on barium sulfate dissolution. Free barium sulfate crystals incubated on the roller table dissolved even more rapidly than crystals in the static experiment (19 ± 7 pg BaSO4 day−1), but barium sulfate crystals incubated with organic matter aggregates showed little sign of dissolution over time. Our findings suggest that organic matter aggregates play a vital role in shielding pelagic barite from dissolution in the water column. This implies that pelagic barite in ocean sediments records the arrival of organic detritus to the seafloor, not just barite crystal formation in sinking organic matter in the upper water column. Additional work is needed to determine which aspects of the marine carbon cycle the pelagic barite proxy captures.

Nanoscale Pathway of Modern Dolomite Formation in a Shallow, Alkaline Lake.

Dolomite [CaMg(CO3)2] formation under Earth surface conditions is considered largely inhibited, yet protodolomite (with a composition similar to dolomite but lacking cation ordering), and in some cases also dolomite, was documented in modern shallow marine and lacustrine, evaporative environments. Authigenic carbonate mud from Lake Neusiedl, a shallow, episodically evaporative lake in Austria consists mainly of Mg-calcite with zoning of Mg-rich and Mg-poor regions in μm-sized crystals. Within the Mg-rich regions, high-resolution transmission electron microscopy revealed < 5-nm-sized domains with dolomitic ordering, i.e., alternating lattice planes of Ca and Mg, in coherent orientation with the surrounding protodolomite. The calcite with less abundant Mg does not show such domains but is characterized by pitted surfaces and voids as a sign of dissolution. These observations suggest that protodolomite may overgrow Mg-calcite as a result of the changing chemistry of the lake water. During this process, oscillating concentrations (in particular of Mg and Ca) at the recrystallization front may have induced dissolution of Mg-calcite and growth of nanoscale domains of dolomite, which subsequently became incorporated as ordered domains in coherent orientation within less ordered regions. It is suggested that this crystallization pathway is capable of overcoming, at least at the nanoscale, the kinetic barrier to dolomite formation.

Clinical study of a new biodegradable magnesium internal fixation screw in treatment of osteonecrosis of the femoral head

To investigate the safety and efficacy of a new biodegradable magnesium internal fixation screw for vascularized iliac bone flap grafting in treatment of osteonecrosis of the femoral head (ONFH). Patients with ONFH admitted between July 2020 and February 2021 were selected as the research objects, and 20 patients (20 hips) met the selection criteria and were included in the study. The patients were divided into two groups ( n=10) by central random method. The iliac bone flap was fixed with a new biodegradable magnesium internal fixation screw in the trial group, and the iliac bone flap was wedged directly in the control group. There was no significant difference ( P>0.05) in gender, age, and side, type, Association Research Circulation Osseous (ARCO) stage, and disease duration of ONFH between the two groups. The operation time and intraoperative blood loss of the two groups were recorded. Laboratory tests were performed at each time point before and after operation, including white blood cell (WBC), electrolytes (K, Ca, P, Mg), blood urea nitrogen (BUN), serum creatinine (Scr), glomerular filtration rate (eGFR), lymphocyte ratio (CD4/CD8), immunoglobulin G (IgG), IgM, alanine transaminase (ALT), aspartate aminotransferase (AST). After operation, Harris score was used to evaluate the hip joint function. CT of the hip joint and X-ray films in anteroposterior and frog positions of the pelvis were used to review the iliac bone flap position, fusion, and screw biodegradation in the trial group. The vital signs of the two groups were stable, the incisions healed by first intention, and no adverse events occurred after operation. One patient in the control group refused to return to the hospital for follow-up at 3 months after operation, and 1 patient in the trial group refused to return to the hospital for follow-up at 1 year after operation. The rest of the patients completed the follow-up at 2 weeks, 3 months, 6 months, and 1 year after operation. Laboratory tests showed that there was no significant difference in WBC, electrolytes (K, Ca, P, Mg), BUN, Scr, eGFR, CD4/CD8, IgG, IgM, ALT, and AST between the two groups at each time point before and after operation ( P>0.05). The operation time and intraoperative blood loss of the trial group were significantly less than those of the control group ( P<0.05). The Harris scores of the two groups at 1 year significantly increased when compared with the values before operation and at 6 months after operation ( P<0.05). There was no significant difference in Harris score between the two groups at each time point ( P>0.05). Postoperative CT of hip joint and X-ray films of pelvis showed that the iliac bone flap reached osseous fusion with the fenestration of the head and neck junction of femoral head in the two groups at 1 year after operation, and no loosening or shedding of iliac bone flap was observed during follow-up. In the trial group, there were signs of dissolution and absorption of the new biodegradable magnesium internal fixation screws after operation, and the diameter of the screws gradually decreased ( P<0.05); no screw breakage or detachment occurred during follow-up. In the treatment of ONFH with vascularized iliac bone flap grafting, the new biodegradable magnesium internal fixation screws can fix the iliac bone flap firmly. Compared with the traditional iliac bone flap wedging directly, it has a shorter operation time, less intraoperative blood loss, and can obtain similar joint function.

Nano-carbide strengthened as-welded joint for precipitation-hardened austenitic Fe–Mn–Al–C lightweight alloys

To date, fusion welding the precipitation-hardened austenitic Fe–Mn–Al–C lightweight alloys still remains an insurmountable challenge. In the present study, the viability of using a Fe-28.3Mn-10.2Al-1.62C (in wt.% hereafter) as a welding filler wire for gas tungsten arc welding (GTAW) of as-hot-rolled Fe-29.2Mn-8.8Al-1.65C base material (BM) were systematically investigated. It was striking that in the as-welded condition, a high density of nano-sized κ-carbide precipitates was formed by spinodal decomposition within the significantly refined austenite dendrite cells in the fusion zone (FZ). This unique feature is critical to achieve a high weld strength in virtually all fusion welded precipitation-hardened alloys. In the heat-affected zone (HAZ), the strengthening nano-sized κ-carbides originally existed in the BM was also preserved with no sign of dissolution or noticeable coarsening. Consequently, the as-welded joint exhibited a fairly uniform microhardness across the FZ, HAZ and BM. More significantly, the entire as-welded joint is free of any solidification cracking and/or liquation cracking. The as-welded joint also exhibited an excellent combination of yield strength, ultimate tensile strength and ductility.

LIFUS II corrosion loop final design and screening of an Al based diffusion coating in stagnant LLE environment

Corrosion phenomena of structural material in Lead-Lithium Eutectic (LLE) environment is influenced by the coolant chemistry, temperature, velocity profile and impurities concentration dissolved in it. In the framework of the EUROfusion consortium, the Experimental Engineering Division (FSN-ING) by the ENEA Brasimone Research Centre (RC) is developing scientific activities to investigate the corrosion rate of materials and to test Al based diffusion coating at 550 °C, different velocities (0.01, 0.1 and 1 m/s) and different exposure times. To this end, a new experimental facility, named LIFUS II (Lithium for Fusion II) is under construction at the Brasimone RC laboratories. Piping and components installed in the hot leg of the facility are internally coated by an Al based diffusion coating developed in collaboration with RINA Consulting-CSM to reduce concentration of corrosion product in the loop. A preliminary screening of the coating was performed in LLE stagnant conditions at 550 °C for 1000 h showing a good resistance and no signs of dissolution were detected. The only modification on the surface was found to be related to the formation of dark islands made of Al2O3.

Pleistocene Evolution of a Scandinavian Plateau Landscape

AbstractThe origins and Pleistocene evolution of plateau landscapes along passive continental margins of the North Atlantic have been debated for more than a century. A key question in this debate concerns whether glacial and periglacial surface processes have substantially eroded plateau areas during late Cenozoic climatic cooling or whether the plateaus have mainly been protected from erosion by cold‐based and largely nonerosive ice sheets. Here we investigate the Pleistocene evolution of a prominent plateau landscape in Reinheimen National Park, southern Norway. We estimate erosion rates across the plateau via inverse modeling of 141 new cosmogenic 10Be and 26Al measurements in regolith profiles and bedrock. We combine these results with sedimentological analyses of the regolith. In the vicinity of Reinheimen's regolith‐covered summits, the combination of uniformly slow erosion (&lt;10 m/Myr) and near‐parabolic slope geometry suggests long‐term equilibrium with the presently active periglacial mass‐wasting processes. Outside summit areas, erosion is faster (up to &gt;50 m/Myr), possibly due to episodic glacial erosion. Despite some indications of chemical alteration, such as grusic saprolite and small amounts of secondary minerals, the fine regolith comprises low clay/silt ratios and is dominated by primary minerals with no sign of dissolution. Together with our modeled erosion rates, this indicates that the regolith cover formed, and continues to develop, during the cold climate of the Late Pleistocene.

Outer organic layer and internal repair mechanism protects pteropod Limacina helicina from ocean acidification

Scarred shells of polar pteropod Limacina helicina collected from the Greenland Sea in June 2012 reveal a history of damage, most likely failed predation, in earlier life stages. Evidence of shell fracture and subsequent re-growth is commonly observed in specimens recovered from the sub-Arctic and further afield. However, at one site within sea–ice on the Greenland shelf, shells that had been subject to mechanical damage were also found to exhibit considerable dissolution. It was evident that shell dissolution was localised to areas where the organic, periostracal sheet that covers the outer shell had been damaged at some earlier stage during the animal’s life. Where the periostracum remained intact, the shell appeared pristine with no sign of dissolution. Specimens which appeared to be pristine following collection were incubated for four days. Scarring of shells that received periostracal damage during collection only became evident in specimens that were incubated in waters undersaturated with respect to aragonite, ΩAr≤1. While the waters from which the damaged specimens were collected at the Greenland Sea sea–ice margin were not ΩAr≤1, the water column did exhibit the lowest ΩAr values observed in the Greenland and Barents Seas, and was likely to have approached ΩAr≤1 during the winter months. We demonstrate that L. helicina shells are only susceptible to dissolution where both the periostracum has been breached and the aragonite beneath the breach is exposed to waters of ΩAr≤1. Exposure of multiple layers of aragonite in areas of deep dissolution indicate that, as with many molluscs, L. helicina is able to patch up dissolution damage to the shell by secreting additional aragonite internally and maintain their shell. We conclude that, unless breached, the periostracum provides an effective shield for pteropod shells against dissolution in waters ΩAr≤1, and when dissolution does occur the animal has an effective means of self-repair. We suggest that future studies of pteropod shell condition are undertaken on specimens from which the periostracum has not been removed in preparation.

Variation of magnetic properties in sediments from Lake Towuti, Indonesia, and its paleoclimatic significance

We investigated the mineral-magnetic behavior of sediments from Lake Towuti located in the Eastern Sulawesi Ophiolite belt, Indonesia. Rock magnetic analysis supplemented by X-ray diffraction and scanning electron microscopy analysis were performed on sediment core TOW10-9B from the north basin of Lake Towuti to give insights on the environmental and sedimentary processes controlling the magnetic properties of the sediment and its paleoclimatic significance. The results show that the core has three distinct zones of varying magnetic properties. Careful examination demonstrates that these zones correspond to varying levels of iron oxide dissolution and magnetite precipitation that are climatically and environmentally dependent. The magnetically strongest zone is characterized by weak iron oxide dissolution and intense magnetite precipitation, likely driven by changes in the stratification and/or water level of the lake during dry conditions in Marine Isotope Stage 2 (MIS2) period, whereas the two magnetically weaker zones are characterized by signs of dissolution and correspond to relatively wet conditions, respectively, during Marine Isotope Stage 3 (MIS3) and the Holocene. Although our data show that major changes in concentration dependent parameters, such as magnetic susceptibility and saturation isothermal remanent magnetization (SIRM), in Lake Towuti sediment correlate with changes in regional rainfall, many of the concentration changes are more strongly affected by in situ chemical processes than by changes in erosion and terrestrial sediment supply. These findings urge caution in the interpretation of magnetic mineral concentration profiles as indicators of clastic sediment inputs.

Zirconium on Benthic Foraminiferal Tests in the Arctic: A Plausible Shield towards Ocean Acidification

Foraminiferal samples from Kongsfjorden (Arctic Ocean) were analysed for elemental ratios using Energy Dispersive spectrometry (EDS), along with sediment organic carbon, grain size and trace metals (Zr and Hf). EDS results on benthic foraminifera N. labradorica tests surface indicated presence of zirconium (Zr), whereas other foraminiferal species like Elphidium excavatum, Cassidulina reniforme and Quinqueloculina stalkeri were devoid of any Zr traces. Both foraminiferal analysis (EDS) as well as sediment analysis (ICP-MS) indicated highest Zr percentage at the inner fjord station 4. Concentration of Zr showed opposite trend to salinity, temperature and organic carbon indicating that the source of Zr is through weathering of continental zircon. Zr showed close association with Hafnium (Hf) and the average Zr/Hf ratio within Kongsfjorden was 43. Benthic foraminiferal shells did not show any signs of dissolution. As Zr is resistant to any acid corrosion; it could possibly be protecting the foraminifera from dissolution. Hence, in the present study we conducted lab experiment on the benthic foraminifera from outer/ inner fjord by pH manipulation, to identify the possible effects on benthic foraminiferal tests in absence/presence of zirconium coating towards dissolution. Interestingly, at pH 6 foraminifera from inner fjord having Zr coating (as evidenced by EDS) did not show any dissolution, whereas outer fjord ones which are devoid of Zr shielding showed dissolution. These preliminary results indicate that with the continuing increase in atmospheric CO 2 it may be interesting to study the test structure of Zr encrusted foraminiferal tests in Kongsfjorden.

Functionalization and Environmental Stabilization of ZnO Nanobridge Sensors Fabricated using Carbonized Photoresist

ABSTRACTZnO nanobridge sensors were selectively grown and electrically connected using lithographically patterned carbonized photoresist (C-PR). As ZnO is known to dissolve in deionized (DI) water, parylene-A was investigated as a moisture barrier and potential functionalization platform. A chemical vapor deposition (CVD) process for parylene-A was developed and it was demonstrated that parylene-A coated ZnO NWs do not show any signs of dissolution after 24 hours in an aqueous solution. The impact of the parylene-A coating on the electrical performance and sensitivity of ZnO nanobridge devices was investigated. A comparison of UV, O2, and H2O sensitivity between uncoated and coated devices revealed that a thin coating of parylene-A attenuated all of these responses, suggesting the ability to modulate environmental sensitivity using this non-covalently bound polymer passivation layer.

Morphology and mineralogy of weathering crusts on highly porous oolitic limestones, a case study from Budapest

Black crusts are very common on limestones in polluted urban environments, but white crusts are less frequently developed. On the soft, porous and inherently weak oolitic limestone of Budapest both crusts are frequent, and indeed white ones are more common on the stone walls of the studied fortress. In this paper, black and white crusts and the host rock have been described using morphological criteria, mineralogical analyses (XRD, DTA), elements analyses (microprobe) and micro-morphological (SEM) tests. The analyses have shown that on white crusts the surface dissolution is combined with the precipitation of gypsum and calcite in the pores and accumulation of gypsum on the underside of the crust. Thin white crusts are removed by a combination of salt crystallisation (gypsum) and frost action while very thick stone layers scale off due to freeze-thaw cycles. Black crusts are enriched in gypsum relative to white crusts. Gypsum accumulates on the crust surface and signs of dissolution have not been observed. Airborne particulates (flyash, silt-sized quartz, and organic debris) adhere to the crust surface of sheltered black crusts. These particles are later incorporated into the expanding gypsum crystals, that are visible on the underside of the crust. The host rock also contains gypsum, but it is washed off the surface when the crust is removed. Further exposure of the host rock may lead to the dissolution of calcite crystals as it is observed by SEM. The micro-environment influences the crust formation and adherence of the crusts. On frequently wet and dry surfaces crust removal is more common. The crust serves as a protective layer on the stone surface, but this protection is temporary since trigger mechanisms such as salt crystallisation or frost action can cause rapid surface loss.

On the nature of the calcareous substrate of a ferromanganese crust from the Vityaz Fracture Zone, Central Indian Ridge: inferences on paleoceanography

A 15-cm-thick carbonate substrate encrusted with ferromanganese oxides from the Vityaz Fracture Zone, Central Indian Ridge was analyzed to reconstruct the paleoceanography of the region. Based on the calcareous nannoplankton assemblage, an early Pliocene age has been assigned to the calcareous substrate. Among the nannoplankton, discoasters outnumber coccoliths and show signs of dissolution. The presence of certain species of benthic Foraminifera such as Uvigerina, Lenticulina, Bulimina and Bolivina, indicates the infringement of the oxygen minimum zone during the deposition of the carbonates. The occurrence of a Reticulofenestra pseudoumbilica zone of early Pliocene age suggests a change in depositional conditions coinciding with the time of formation of the large depositional hiatuses documented in sediment cores from adjacent basins of the western Indian Ocean. These hiatuses resulted from the prevalence of intermediate subsurface currents such as the Somali Current or the Western Boundary Current.

Corrosion behavior of steels in flowing lead–bismuth

Corrosion of steels in a flowing Pb–Bi environment has been studied. Specimens were exposed to the melt at 300°C and 470°C for up to 3116 h. The flow velocity was close to 2 m/s and the oxygen concentration in Pb–Bi was maintained at 1–2×10 −6 wt% . Independent of the specific steels (Optifer IV, T91 and EP823 martensitic steels, 1.4970 austenitic steel), no sign of dissolution was detected for either temperatures. In all cases, a protective oxide layer was formed on the steel surface. It was very thin (thickness ≪1 μm ) in the case of the 1.4970 austenitic steel, which presented the maximum resistance to oxidation in Pb–Bi–O. After 3116 h at 470°C, the thickness of the oxide layer (magnetite scale Fe 3O 4) formed on the martensitic steels ranged from about 10 to 20 μm. The oxidation resistance of the three martensitic steels decreases in the sequence: EP823, T91 and Optifer IV. The presence of silicon in the EP823 Russian steel (≈2 wt%) reduces the oxide layer growth. Results show that the present level of oxygen content in Pb–Bi is suitable for ensuring stable protection of steels against liquid metal corrosion at least for that period.

Antagonic-stress: A therapeutic composition for deceleration of aging. II. Brain lipofuscinolytic activity demonstrated by electron microscopy

Electron microscopic morphology and distribution of brain lipofuscin and ceroid (LP) were studied after 8 weeks of daily treatment with Antagonic-Stress (AS), a new combination of various components with cerebroprotective and anti-aging properties. LP characteristics were investigated in selected brain areas of control adult (CA), control old (CO) and treated old (TO) groups of 30 male Wistar rats. Cellular and regional distributions of LP in the TO group were very different from those of the CO group and resembled that of the CA group. In addition, electron microscopic signs of dissolution of LP were constantly observed in the TO group. Neurons and glia cells of TO group displayed an intense replacement of damaged organelles, especially of mitochondria, with normal organelles, many of them in hyperfunctional stages. Neuronal, glial and capillary LP lysis occurred simultaneously with neuro-glial LP transfer and capillary LP elimination. Numerous microglia cells overloaded with processed LP were identified in the vicinity of the capillary areas. AS treatment of 8 weeks induces lysis of LP which may be useful for therapeutic purposes in various brain pathologies and in deceleration of brain aging in healthy elderly.

Fresh Water and Acid Sensitivity of Authigenic Clays in Sandstone Reservoirs

Authigenic illite-smectite and chlorite in reservoir sandstones from several Pacific rim sedimentary basins in Australia and New Zealand have been examined using an Electroscan Environmental Scanning Electron Microscope (ESEM) before, during, and after treatment with fresh water and HCl, respectively. These dynamic experiments are possible in the ESEM because, unlike conventional SEMs that require a high vacuum in the sample chamber (10-6 torr), the ESEM will operate at high pressures up to 20 torr. This means that materials and processes can be examined at high magnifications in their natural states, wet or dry, and over a range of temperatures (-20 to 1000 degrees C) and pressures. Sandstones containing the illite-smectite (60-70% illite interlayers) were flushed with fresh water for periods of up to 12 hours. Close examination of the same illite-smectite lines or filled pores, both before and after freshwater treatments, showed that the morphology of the illite-smectite was not changed by prolonged freshwater treatment. Chlorite-bearing sandstones (Fe-rich chlorite) were reacted with 1M to 10M HCl at temperatures of up to 80 degrees C and for periods of up to 48 hours. Before treatment the chlorites showed typically platy morphologies. After HCl treatment the chlorite grains were coated with an amorphous gel composed of Ca, Cl, and possibly amorphous Si, as determined by EDS analyses on the freshly treated rock surface. Brief washing in water removed this surface coating and revealed apparently unchanged chlorite showing no signs of dissolution or acid attack. However, although the chlorite showed no morphological changes, elemental analysis only detected silicon and oxygen.

Almandine in Thermal Aureoles

The concept that almandine-rich garnet is an anomalous phase in thermal metamorphic assemblages is based partly upon the rarity of almandine in hornfelses, and partly upon evidence of breakdown of ‘regionally’ formed garnets when their host-rocks have been thermally metamorphosed. Where amphibolite facies regional gneisses have been re-metamorphosed within the pyroxene-hornfels facies conditions of the late Caledonian Lochnagar aureole, garnet of composition Alm80Py11p6 (Gr+And)4 has reacted with biotite, sillimanite, and muscovite to give cordierite-rich pseudomorphs; where armoured from reaction by immersion in quartz or feldspar, no signs of dissolution are seen. In some totally reconstituted hornfelses, almandine garnet of composition AIm80P13Sp4 (Gr+And)3 appears to have coexisted stably with cordierite and orthoclase. It is concluded that the ‘unstable’ garnet was breaking down not because its P/T stability field had been exceeded, but because the alman-dine-bearing rock-composition field in the thermal (pyroxene-hornfels) facies was more restricted than that in the regional (amphibolite) facies. Chemical data from the hornfelses suggest that this restriction was mainly due to the stability of cordierite—the plane spinel-cordierite-quartz restricts garnet to those rocks with effective mol. (FeO+MgO-t-MnO) A12O3>1, while within that range cordierite-biotite tie-lines restrict garnet to rocks of high (FeO+MnO)/MgO ratio (Fig. 4b). Recorded instances of garnet ‘instability’ in thermal aureoles show similar features to the Lochnagar aureole—garnet breaks down by reaction; unequivocal instances of isochemical breakdown are rare. This, combined with the widespread occurrence of almandine in volcanic and plutonic igneous rocks, suggests that almandine is a physically stable phase not only in the hornblende-hornfels facies, but also in the pyroxene-hornfels facies and possibly in portion of the sanidinite facies as well. The rarity of almandine in thermal aureoles is the result of its very narrow rock composition field under the P/T conditions of such environments. Comparison of thermal and granulite facies garnet-cordierite assemblages suggests that P and T modify the almandine-bearing rock composition field mainly by modifying the limiting Mg/Fe ratio of garnet and the limiting Fe/Mg ratio of cordierite (Fig. 10). The wide rock-composition field of almandine in the amphibolite facies may be contingent upon the inhibition of cordierite by hydrous minerals under relatively high partial pressures of water.