Pb Diffusion Research Articles

Effect of Si doping on elastic-plastic fracture toughness (JIC) of T91 ferritic/martensitic steel in liquid lead-bismuth eutectic

This work was devoted to understanding the effect of Si doping (1.27 wt%) on elastic-plastic fracture toughness (JIC) of T91 ferritic/martensitic (F/M) steel in liquid lead-bismuth eutectic (LBE, Pb44.5Bi55.5, wt%) under various parameters. The results showed that Si doping significantly promoted occurrence of liquid metal embrittlement (LME) and led to more severe degradation of fracture toughness at 350 °C, especially in oxygen-poor LBE. The LME susceptibility of T91-Si steel was found to be nearly independent on the loading speeds, while T91 F/M steel exhibited a stronger LME effect when the loading speed was decreased from 0.02 mm/min to 0.002 mm/min. Oxygen concentration had a mild effect. Detailed microstructural analyses showed that the fracture behavior of the T91-Si steel in LBE environment at 350 °C was analogous to cleavage fracture and the crack propagation was mainly transgranular. The crack wall was quite rough and locally faceted to low-index crystallographic planes of {110}. Numerous dislocations were also present in the vicinity of the crack tip. No solid evidence of diffusion of Pb and Bi into the steel bulk was discovered even at the atomic scale, which strongly suggests a crack tip surface adsorption-based LME mechanism.

U−Pb geochronology and microstructural analysis of apatite within a Proterozoic crustal-scale shear zone, Outer Hebrides, NW Scotland

U–Pb apatite geochronology is increasingly recognized as a valuable tool for constraining the age of mid-crustal ductile shear zones. The crustal-scale Outer Hebrides Fault Zone (OHFZ) within the Laurentian foreland of the Scottish Caledonides has long been of uncertain age and tectonic significance. Earliest deformation within the OHFZ was associated with top-to-the-NW ductile thrusting that formed a belt of greenschist facies mylonites within host Archean−Paleoproterozoic basement gneisses. Previous estimates for the timing of thrusting vary between c . 1600 Ma and c . 430 Ma. The mylonitic fabrics are defined by a recrystallized assemblage of quartz + albite/oligoclase + sericite + actinolite + epidote + apatite ± calcite, consistent with deformation temperatures of 400–500°C and within the range of reported closure temperatures for Pb diffusion in apatite. U–Pb (LA−ICP−MS) dating of two texturally distinct apatite grain types within the mylonites has yielded ages mostly in the range c . 1100–900 Ma. The OHFZ is therefore interpreted as a Grenville–Sveconorwegian structure that formed during the tripartite collision of Laurentia, Baltica, and Amazonia and the assembly of Rodinia. Supplementary material : U–Pb isotopic data (Table S1), trace element data (Table S2) and laser ablation spot images are available at https://doi.org/10.6084/m9.figshare.c.7084925

Disparate Pb-isotopic ages of silicate and phosphate minerals in the diabasic angrite Northwest Africa 12320

Pb-isotopic dating of the recently discovered diabasic angrite Northwest Africa (NWA) 12320 yielded ages of 4564.17 ± 0.50 Ma and 4562.82 ± 0.37 Ma for acid-insoluble and soluble minerals respectively. These ages are calculated using measured 238U/235U ratios of soluble and insoluble minerals, thereby excluding the possibility that the apparent age difference is caused by internal U-isotopic variations. The age of the insoluble minerals is indistinguishable from published Pb isotopic ages of other medium-grained angrites SAH 99555 and D'Orbigny. The age of acid-soluble minerals is distinctly younger, with a 1.35 ± 0.62 Ma age gap between the PbPb ages of the two mineral fractions. The mineral hosts of U, Th and radiogenic Pb in the meteorite were identified through in-situ SIMS measurements of these elements in all minerals. The principal carriers of U, Th and radiogenic Pb are acid insoluble Al-Ti-rich augite and soluble Si-rich phosphate. Closure temperatures for diffusion of radiogenic Pb in these minerals are calculated to be respectively 820 ± 90 °C and 450 ± 80 °C using the observed range of crystal dimensions and the published experimental data for Pb diffusion in augite and apatite. The age difference between the pyroxene and phosphates has two potential explanations: (1) a late reheating event >450 °C which may have re-set the UPb systematics of the phosphates but not the pyroxenes or (2) slow cooling of the rock from ∼450–820 °C. If slow cooling is the reason for the age difference, we can estimate a model cooling rate of 270 ± 150 °C/Ma over the estimated closure temperature range between pyroxenes and phosphates. This rate is ∼11 orders of magnitude slower than petrologic cooling rates of quenched angrites at temperatures above 1000 °C determined experimentally using the composition of Asuka 881371 groundmass (Keil, 2012), which is similar to NWA 12320 groundmass. If there was no late reheating event, the discrepancy between fast cooling rates at high temperatures near the solidus, followed by much slower cooling at lower temperatures, might have been caused by impact melting. It could also be attributed to the initial eruption of the source magma of NWA 12320 near the surface of the parent body, followed by burial due to subsequent eruptions.

Baddeleyite microstructural response to shock metamorphism in three enriched shergottites and implications for U–Pb geochronology

Baddeleyite (monoclinic zirconia; m-ZrO2) occurs as a late-stage accessory mineral in shergottites and has been used to determine U–Pb igneous crystallization ages via in-situ secondary ion mass spectrometry (SIMS). During shergottite ejection from the surface of Mars, baddeleyite develops a range of microstructures primarily due to a series of shock-induced transformations to high pressure and temperature polymorphs. It remains poorly constrained to what extent U–Pb systematics in baddeleyite are sensitive to shock conditions experienced by shergottites. To investigate this, we examined baddeleyite in the enriched shergottites Jiddat al Harasis (JaH) 479, Northwest Africa (NWA) 10299, and NWA 12919, which bridge the gap in shock conditions represented in previous microstructural studies. Electron backscatter diffraction (EBSD) analysis reveals that although some baddeleyite grains retain magmatic microstructures (i.e. homogenous crystallographic orientations and twinning of igneous origin), there is widespread phase transformation to high-pressure orthogonal polymorphs (o-ZrO2) followed by reversion. JaH 479 contains more grains with preserved magmatic microstructures than the other two shergottites, suggesting that it experienced lower bulk shock pressures. Nanometer-scale reverted m-ZrO2 in NWA 10299 and NWA 12919 further points to insufficient post-shock temperatures; this contrasts with JaH 479 where greater variation in local temperature conditions enabled the development of µm-scale domains of reverted m-ZrO2. Individual grains that are separated into two distinct microstructural domains may reflect controls on shock propagation due to relative density contrast among the surrounding phases.SIMS U–Pb baddeleyite analysis yields igneous crystallization ages of 210 ± 9 Ma (JaH 479), 196 ± 11 Ma (NWA 10299), and 188 ± 11 Ma (NWA 12919). At the SIMS resolution, we find no clear evidence for significant Pb loss in the surveyed baddeleyite grains, suggesting that temperatures during the formation of both nm-scale and µm-scale reverted m-ZrO2 in the three shergottites were insufficient to cause significant Pb diffusion. Given the robust baddeleyite U–Pb isotope systematics in the majority of shergottites dated by SIMS methods thus far, we argue that shock conditions experienced by the bulk of shergottites were insufficient to introduce significant U–Pb isotopic mobility, which is limited to grains showing microstructural evidence for extensive post-shock heating and recrystallization. Our findings place new constraints on baddeleyite microstructural response to shock conditions of shergottite ejection and demonstrate that microstructural observations are critical when using baddeleyite as a chronometer in shocked planetary materials.

Probing the degradation pathways in perovskite solar cells

Perovskite solar cells (PSCs) have almost climbed up with established photovoltaic technologies in terms of power conversion efficiency. Hence, it is crucial to understand the operational as well as long-term stability for commercialization. However, stability studies are often conducted in non-standardized and short-term ways, resulting in data that cannot be understood effectively. Additionally, assessing the stability of perovskite solar cells, which have unique properties, may require adjusting common standards. Our research investigates the storage affects the aging of perovskite solar cells for a long period span of 3 years. Glass/FTO/compact-TiO2/mesoporous-TiO2/perovskite/Spiro-OMeTAD/Au structured solar cell devices are fabricated and tested for stability. The power conversion efficiency (PCE) drops significantly from 17 % to 8 % over three years of the stored perovskite solar cells in N2 filled glove box, mainly due to the decomposition of the perovskite layer as confirmed by ToF-SIMS and XRD studies. Interestingly, lead (Pb) diffusion towards metallic contact becomes a dominating factor over time. Photoluminescence studies also confirm strong quenching of the perovskite layers emission spectra due to the defects through ion migration process. Our findings offer a pathway to understanding the longevity of PSCs and additionally provide an opportunity to manufacture large-scale PSCs with the aim of commercialization.

Effect of heterogeneity on the diffusion of Pb in apatite for petrochronological applications: A multiscale approach to characterizing the influence of apatite chemistry and anisotropy on Pb diffusion

The investigation of various factors effecting the Lead (Pb) diffusion in phosphate minerals such as apatite is still challenging in the interpretation of (UTh)/Pb geochronology. For (UTh)/Pb system, apatite minerals have closure temperatures in the range of 375 to 600 °C and therefore can be used for the investigation of mid-temperature thermochronological and/or petrochronological questions i.e., the reconstruction of thermal events in Earth's crust. There is still uncertainty whether Pb diffusion in apatite is characterized by thermally activated volume and/or anisotropic diffusion profiles or is instead impacted by novel growth processes and recrystallization (chemical substitutions). As the apatite structure support extensive compositional variability, including partial or total substitution of both the cationic and anionic sites and forms solid solutions therefore, it necessitates a thorough examination of these effects and anisotropy on Pb diffusivity and (UTh)/Pb geochronometric system. For this, a multi-scale study is carried out to examine the effects of chemical composition, anisotropy, and growth structure on the diffusion of Pb in order to better understand the behaviour of Pb diffusion in apatite. This study employed computational techniques like Density Functional Theory (DFT) and Transition State Theory (TST) at the atomic level and integrates it with the Kinetic Monte Carlo (KMC) simulations at the macroscopic level. Models of this study shows that Pb diffusion is completely anisotropic along the preferred z-axis or [001] direction and Pb readily escapes faster from Na-substituted apatite when compared to pure F-apatite and Cl-substituted apatite. Because of this anisotropy and chemical substitutions, Pb diffusivity in apatite either increases by opening of diffusion channels or decreases by blocking the diffusion channels depending on the site and type of chemical substitution. Further, in case of blocking effect the Pb diffusion occurs through workaround pathways and approaches towards the isotropic diffusion. For Na-substituted apatite, the impact of Na occupation on anisotropic Pb diffusion is significantly greater while in case of Cl-substituted apatite the Cl occupation mostly leads towards isotropic diffusion by opening the diffusion paths along other directions (mostly along the in-plane direction). Furthermore, the high closure temperatures (Tc) (e.g., ∼1370 °C) of the modelled apatites (except the perfect Na-substituted apatite e.g., ∼500 °C) of this study when compared to the Tc of Durango apatite obtained experimentally for the effective grain size of 100 μm and cooling rates of 10 °C/Ma indicate that the effective closure temperature dominantly depends on the degree and types of chemical substitutions and play a crucial role for the closure or opening of Pb diffusion/loss in apatites.

Pb diffusion in perfect and defective zircon for thermo/petro-chronological investigations: An atomistic approach

Factors that affect the diffusion of lead (Pb) in zircon are still a debatable issue amongst geochronologists. These are anisotropy, chemical composition, metamictization, radiation damage, and defects such as vacancy and Frenkel pairs. Careful investigations of such effects require a detailed description at atomic levels. This study focuses on the details of Pb diffusion pathways (anisotropy) at the atomic scale level in perfect zircon lattices for the better understanding of thermo/petro-chronological problems in geosciences. The applications of Density Functional Theory (DFT) combined with both the Nudged Elastic Band (NEB) method and Transition State Theory (TST) together with Kinetic Monte Carlo (KMC) simulations provide a reasonable estimate of the activation energy and diffusion of lead (Pb) in a perfect zircon lattice. Results of the tested methodology give the diffusion co-efficient of anisotropic nature in perfect zircon i.e. the activation energies and frequency factors (D0) along the z-axis [001] is 687 kJ/mol and 4.16×10−3cm2/sec, along zx-axis [101]/[011] is 1331 kJ/mol and 8.57×10−4cm2/sec and along the x-axis is 5810 kJ/mol and 8.57×10−4cm2/sec respectively. The Closure temperatures for Pb in perfect zircon lattices are reasonably high for an effective grain size of 60 μm and a cooling history of 10 °C/Ma. This study also demonstrates that the closure temperature is affected not only by the geometry of a given grain, but also by defects and radiation damage. Furthermore, the calculated closure temperatures show poor calibrations with previous experiments of Pb diffusion in natural zircon, implying that radiation damage and vacancies are causing the reduction in Pb diffusion. Therefore, the gap between the computed and experimental results may probably be due to the change in the chemistry of each zircon crystal used in the experiments. This study is useful in characterizing the effect of individual entities on Pb diffusion in zircon, showing good agreement with experiments, and indicating the applicability of DFT + NEB+TST + KMC methods for characterization of Pb diffusion in perfect zircon.

Pb diffusion in magnetite: Dating magnetite crystallization and the timing of remanent magnetization in banded iron formation

The ferrimagnetic mineral magnetite (Fe3O4) is abundant in banded iron formation (BIFs), and has the potential to provide UPb or PbPb age information on these rocks because it incorporates small amounts of U during growth. Combined with age measurements, paleomagnetic studies of BIF magnetites may also yield insight into the history of Earth's magnetic field and its relationship to early evolution of Earth's interior and atmosphere.Reliable magnetite ages utilizing Pb isotopes require knowledge of Pb diffusion in the magnetite structure. For this reason, we undertook an experimental investigation of Pb diffusion in magnetite by diffusing Pb2+ ions into pre-polished slabs of natural magnetite oriented parallel to {001} or {111}. A mixture of PbSO4 and Fe2O3 was used as a surface powder source to supply Pb2+ diffusant at the sample surface and at the same time buffer the oxygen fugacity of the system at magnetite-hematite (MH)—a typical fO2 for banded iron formations (BIFs) due to the common presence of both iron oxides (and where Pb2+ is stable relative to other Pb valence states). Diffusion experiments spanned temperatures of 500–675 °C and durations of 75 to 2035 h. Following each experiment, in-diffused Pb was depth-profiled using Rutherford backscattering spectroscopy (RBS) and Pb diffusivities were calculated from the profiles using an infinite half-space diffusion model. The following diffusion law for Pb2+ in magnetite is based upon 12 independent diffusivity measurements:DPb (m2·s−1) = (9 × 10−17 m2·s−1) exp.(−98,000 J·mol−1)/RT)where the uncertainties in the pre-exponential constant and activation energy are ±6% and ± 15%, respectively.Pb diffusion in magnetite over the temperature range of our study is orders of magnitude slower than projected for other divalent cations based on down-temperature extrapolation of previously measured diffusion laws (e.g., for Mn2+, Fe2+, Co2+, and Ni2+). This finding is encouraging in terms of the potential suitability of magnetite for UPb age determinations of BIFs and other magnetite-bearing rocks. Indeed, classical Dodson closure temperatures well above 500 °C are not unrealistic in cases where magnetite crystals having large diffusion domains (e.g., >100 μm in radius) are cooled relatively rapidly (e.g., at 100 °C/MYr). This is of particular significance for paleomagnetic studies, since the Curie temperature of magnetite is 580 °C and therefore the age of magnetization in magnetite-bearing rocks may be directly dated. However, slow cooling of magnetites having small diffusion domains can lead to Pb loss at temperatures of 200 °C or lower. Pb mobilization is evaluated for various time-temperature scenarios that involve both heating and cooling as well as “closed-loop” time-temperature paths. We conclude that UPb or PbPb age determinations of BIF magnetites are potentially reliable, but isotopic results should be assessed in concert with knowledge of the thermal history of the host rock and the effective grain size of the magnetites.

The Corrosion Behavior of Al/Al2O3 Composite Films with Ultra-Dense Structure Exposed to Lead-Bismuth Eutectic at 450 to 650 °C

Al2O3 coatings are the most promising candidate material for mitigating (lead-bismuth eutectic) LBE corrosion at elevated temperatures, but preventing inward diffusion of Pb, Bi, and O for the ceramic coating remains a critical challenge. Here, we have fabricated an amorphous Al2O3 coating with an ultra-dense structure by continuous high-power magnetron sputtering (C-HPMS). After LBE corrosion at 550 °C for 2000 h, nanocavities induced by the phase transformation from amorphous to γ-Al2O3 provide the diffusion path for Fe, O, Pb, and Bi in which the corrosion products, such as Fe3O4, PbO2, or their mixed oxides, form. Furthermore, the diffusion of Pb to the substrate and Cr segregation at the interface between the coating and substrate are observed for the sample exposed to LBE at 550 °C for 4000 h. Additionally, the hardness and interface bonding strength are enhanced after LBE corrosion. Moreover, pit corrosion was found to be the main failure mode of coating, and pits that merged with each other induced large area failure at a temperature of 650 °C. The corrosion mechanism of Al2O3 includes element diffusion, phase transformation, and chemical reaction. This work not only provides a deep understanding of the corrosion mechanism of amorphous Al2O3 coatings, but also shows the optimization method on the corrosion resistance of Al2O3 coating.

Understanding the Mechanism for Adsorption of Pb(II) Ions by Cu-BTC Metal-Organic Frameworks.

With the growing population, industrialization, and agriculture, water contamination not only affects people but entire ecosystems. Metal-organic frameworks (MOFs), because of their large surface area and porosity, show great potential as adsorbents for removing pollutants, such as heavy metals, from contaminated water. The current research aims at examining copper (II) benzene-1,3,5-tricarboxylate (Cu-BTC) MOFs and understanding the mechanism for their adsorption of Pb(II) from aqueous solution. The Cu-BTC samples were characterized using FTIR and XRD, and their surface area and porosity were determined based on N2 adsorption isotherms. The concentration of Pb(II) in the solutions was measured using atomic absorption spectroscopy (AAS). Both kinetic and equilibrium adsorption data were collected and then analyzed using numerical models. The analyses led to the findings that the limiting steps in the adsorption of Pb(II) on Cu-BTC are (a) pore diffusion of Pb(II) and (b) the availability of the active sites on Cu-BTC MOFs. It was further revealed that the former step is more dominant in the adsorption of Pb(II) when the lead concentration is low. The latter step, which is directly proportional to the surface areas of the MOFs, affects the adsorption to a greater extent when the lead concentration is high. The results also show that adsorption of Pb(II) ions on Cu-BTC is mainly a multi-layer heterogeneous process.

U–Pb and trace element zircon and apatite petrochronology of eclogites from the Scandinavian Caledonides

The petrochronological records of eclogites in the Scandinavian Caledonides are investigated using EPMA and LA-ICPMS of zircon and apatite for U–Pb geochronology, combined with major and trace element characteristics. Metamorphic zircon from two eclogites from the Lofoten-Vesterålen Complex (Lofoten Archipelago region) collectively yielded a Concordia age 427.8 ± 5.7 Ma and an upper intercept U–Pb age 425 ± 30 Ma. Apatites from the same eclogites provided U–Pb lower intercepts at 322 ± 28 Ma and 354 ± 33 Ma, with the latter also yielding a younger age of 227 ± 24 Ma. Two eclogites from the Lower Seve Nappe (Northern Jämtland) demonstrate different zircon and apatite age records. Metamorphic zircon provided Concordia ages of 467.2 ± 5.9 Ma and 444.5 ± 5.5 Ma, which resolve the age of prograde metamorphism and zircon growth during retrogression, respectively. The lower intercept U–Pb ages of apatites from the same eclogites are 436 ± 18 and 415 ± 25 Ma, respectively. In combination with their geochemical characteristics, they suggest two separate stages of exhumation of eclogite bodies in the Lower Seve Nappe. Zircons from an eclogite from the Blåhø Nappe (Nordøyane Archipelago) yielded a continuum of concordant U–Pb dates from ca. 435 to 395 Ma, which suggests several cycles of HT metamorphism within short intervals. Distinctive trace element characteristics of apatites from the Blåhø Nappe eclogite suggest formation coeval with zircon and garnet during HT metamorphism, but Pb diffusion behaved as an open system until cooling during exhumation of the nappe at 390 ± 12 Ma (lower intercept U–Pb age of apatite). To summarize, this study presents the high potential of coupled zircon and apatite petrochronology of eclogites in resolving their metamorphic evolution, particularly with respect to using trace element characteristics of apatites to constrain the records of their growth, alterations and the meaning of their U–Pb age record.

Municipal Participatory Budgeting Designs in the V4 Countries

Abstract Research on PB in CEE has been rather fragmented and has focused on the diffusion of PB, and sometimes on determinative factors inside the countries. Some comparative studies exist but address primarily initial steps of PB. This paper presents the outcomes of a research that focused on the design of participatory budgeting in the Visegrad countries (Czech Republic, Hungary, Poland, and Slovakia). The main method is a secondary comparative analysis of existing literature and information on the subject. The findings are based on recently published country studies and other available information related to the national context in the countries. We use the country studies as input for a multi‐case study analysis (Zongozzi & Wessels, 2016) to make comparisons and, if possible, generalize some of the findings, but also to point out specifics determined by the context in which PB is being implemented and practiced. As the subsidiary method we used expert evaluation. To obtain extra information we consulted experts in all selected countries during July and August 2022. Analyzing PB processes in these countries showed similar features and that, on the whole, PB processes still belong to the group o the Porto Alegre model adapted for Europe as concluded in the literature published almost a decade ago. But this is only valid at a more abstract level of PB designs. Looking at PB processes in practice, it is seen in the V4 region that the actual practices vary over municipalities, even within one and the same country.

Evolution of the neoarchean Kola alkaline granites, northeastern Fennoscandian Shield: insights from SHRIMP-II titanite and zircon U–Pb isotope and rare earth elements data

Abstract An U–Pb isotopic investigation combined with rare earth element data for titanites, zircons and coexisting accessories has been undertaken to gain insight into the formation of the Archean peralkaline granites of the northeastern Fennoscandian Shield and to test the stability of titanite during metamorphic and hydrothermal processes. The obtained set of isotope data shows that whereas more stable zircon retains a memory of the major episodes of granite evolution, the coexisting titanite provides additional information on crystallization, subsequent growth, cooling and alteration of the plutonic complexes. In addition to titanites formed at the magmatic stages of c. 2710 and c. 2650 Ma, the peralkaline granites contain titanite populations which have undergone major resetting at c. 1870 Ma during the burial metamorphism related to the Svecofennian orogeny and the 1760 Ma hydrothermal alteration near contemporaneous with regional metamorphism of c. 1780 Ma. The peralkaline granites which contain c. 2710 Ma titanites also include inherited titanite grains of an age of 2795 Ma. These data support the concept that the titanite can remain a closed system to Pb diffusion at temperatures of peralkaline granite melt (<800°C) as long as the crystals escape magmatic or metamorphic recrystallization.

Stencil printing and sintering formation performance of tempered vacuum glazing support pillar

PbO-TiO2-CaO-SiO2-RxOy glass powder slurry was printed on the surface of a tempered glass sheet by stencil and made into support pillars inside the vacuum glazing by sintering method. The molding parameters and microstructure of sintered formed support pillars(SFSP) were measured and observed, and the mechanical properties of SFSP were simulated by ANSYS. The forming results showed that the best forming parameters were obtained for the support pillars at a sintering temperature of 380 °C. The EDS results showed that the diffusion of Pb and Ti elements from the glass powder into the glass flakes occurred during sintering. The SEM results showed that the organizational structure of SFSP became more uniform and dense when the sintering temperature increased from 360 ℃ to 380 ℃. When the sintering temperature continued to increase, lots of crystalline material precipitated in SFSP and even produced holes. The analysis results of XRD showed that the crystal structure of SFSP was mainly composed of Pb0.6875Ca0.3125TiO3, which has the highest crystallinity and content at the sintering temperature of 380 ℃, and the structural strength and denseness of SFSP were good. The simulation results showed no significant difference between SFSP and stainless steel support pillars(SSSP) on the stress and deformation of tempered vacuum glazing(TVG). The SFSP could meet the safety requirement and optimize effects on reducing the stress on the support pillars.

Ag and Pb diffusion on Ge(111)-3x2sqrt(3)sqrtSn surface

Ag and Pb diffusion on Ge(111)-3x2sqrt(3)sqrtSn surface has been studied by Auger electron spectroscopy and low energy electron diffraction. The mechanism of diffusion of atoms of these elements along the Ge(111)-3x2sqrt(3)sqrtSn surface is determined, and the temperature dependences of the diffusion coefficients are measured. The diffusion parameters of Ag along the Ge(111)-3x2sqrt(3)sqrtSn and Si(111)-2sqrt(3)sqrtSn surfaces are compared. Keywords: surface, surface diffusion, Ge(111), Ag, Pb, Sn.

Диффузия Ag и Pb по поверхности Ge(111)-3x2sqrt(3)sqrtSn

Ag and Pb diffusion on Ge(111)-3x2sqrt(3)-Sn surface has been studied by Auger electron spectroscopy and low energy electron. The mechanisms of diffusion of atoms of these elements along the Ge(111)-3x2sqrt(3)-Sn surface are determined, and the temperature dependences of the diffusion coefficients are measured. Surface diffusion coefficients versus temperature have been measured. The diffusion parameters of Ag along the Ge(111)-3x2sqrt(3)-Sn and Si (111)-2sqrt(3)x2sqrt(3)-Sn surfaces are compared.

Evolution of erythrocyte and urine lead concentrations after cutaneous exposure to mud packs embedded into micro-perforated polyethylene bags according to the protocol used in French medical spas

Lead (Pb) is an environmental pollutant which may cause harmful effects on human health. It may be present within the mud-packs deposed on patient'skin for treating some rheumatologic conditions. We aimed to evaluate the diffusion of Pb from therapeutic mud-packs toward the human body in order to exclude safety concerns.We quantified Pb using inductively-coupled plasma mass spectrometry in blood (erythrocytes) and urine (raw concentration and divided by creatinine concentration) of 35 young healthy volunteers before and after the 21-day pelotherapy procedure from French medical spas (i.e hot micro-perforated polyethylene bags embedded-mud packs soaked in mineral water and deposed during 10 min on five cutaneous sites, in 5-day sequences during 3 consecutive weeks). We did not evidence a significant increase in their erythrocyte (p: 0.89) or urine (p: 0.96) concentrations when comparing pre- and post-treatment samples by the bilateral apparied Student test. These levels were markedly inferior to the recommended cut-off in all our participants taking into account the exclusion of individuals with extreme urinary creatinine values. From our sample including individuals with an optimal transcutaneous diffusion capacity (young persons with low subcutaneous fat mass) we conclude that there is no risk of Pb overexposure in patients receiving this type of pelotherapy regimen.

Removal of Pb(II) from water samples using surface modified core/shell CdZnS/ZnS QDs as adsorbents: Characterization, adsorption, kinetic and thermodynamic studies

This research presents aqueous colloidal method to synthesize CdZnS/ZnS surface modified core/shell quantum dots (QDs) with capping agents 2-mercaptoacetic acid and 3-mercaptopropanoic acid. The QDs were characterized by the different analytical techniques. Using Plackett–Burman and Central composite designs, optimum conditions for the removal of Pb(II) from aqueous medium were developed: QDs (0.013 g) at pH 6.9, time of adsorption and desorption (20 min), temperature (61.1 °C) and dilution on 100 ppb standard solutions. Moreover, Freundlich models suggested that Pb(II) adsorption was favorable on the heterogeneous surface of QDs. The values of Δ G ° and Δ H ° (−59.26 KJ/mol.K) suggested the process was spontaneous and exothermic. The negative Δ S ° (−0.16 KJ/mol.K) indicates that the Pb(II) chemisorb on QDs. While, system follows the pseudo-second order rate equation which indicates that rate limiting step involves chemical reaction and could be influenced by the intraparticle/pore diffusion of Pb(II) ions with QDs. By using atomic absorption spectrophotometer, developed method was tested for Pb(II) removal from tap and ground water samples taken from the different districts of Karachi City. The % recovery for Pb(II) was found to be 96.4 % (tap water) and 94.8 % (ground water) with LOD = 0.1 ng mL −1 and LOQ = 0.90 ng mL −1 .

An improvement of low temperature characteristics of an La-doped Pb(Zr,Ti)O3 capacitor

We developed a lanthanum-doped Pb(Zr0.4,Ti0.6)O3 (PLZT)-based ferroelectric capacitor (FE) aiming at low-voltage operation of ferroelectric random access memory at low temperatures down to −45 °C. High-temperature sputter-deposited IrO x (1 < x < 2) or HT-IrO x was employed as a top electrode (TE) instead of room-temperature (RT) deposited IrO x or RT-IrO x over two PLZT stacked layers. We observed that polarization characteristics drastically improved even at −45 °C by employing HT-IrO x and thinning PLZT, even though leakage current was increased by about one order of magnitude. Transmission electron microscopy observations showed that HT-IrO x has a columnar-like crystalline structure while RT-IrO x has a granular-like crystalline structure. Secondary ion mass spectroscopy indicated that Pb diffusion from PLZT into TE was suppressed by HT-IrO x , which is considered to cause the improvement of polarization characteristics.

Use of Eggshell-Catalyzed Biochar Adsorbents for Pb Removal from Aqueous Solution.

Eggshell is a cheap and environmentally friendly calcium source. In this study, Ca-modified biochar adsorbents (CEA) were prepared by 1:10, 1:2, and 1:1 mass ratio of the eggshell and Eupatorium adenophorum. The CEA-2 sample prepared with a 1:2 mass ratio showed a maximum Pb adsorption capacity (97.74 mg·g–1) at the conditions of an initial pH of 7.0, an adsorbent dosage of 0.5 g·L–1, and a contact time of 8.0 h. The kinetic and isotherm studies indicated that the adsorption process of the CEA-2 sample had monolayer adsorption characteristics, which was controlled together by intraparticle and interface diffusion. Thermodynamic studies indicated that the adsorption process of CEA-2 was spontaneous (ΔG0 <0) and endothermic (ΔH0 > 0). X-ray diffraction and scanning electron microscopy analyses showed a uniform distribution of Ca–Pb precipitation on the CEA-2 surface, which proved that chemical precipitation was the main adsorption mechanism. Fourier transform infrared spectra found that CEA-2 had abundant active groups, especially nitrogen-containing functional groups, which could adsorb Pb through a surface complexation reaction. The Brunauer–Emmett–Teller surface area of CEA-2 was found to be 621 m2·g–1, and such developed pores could ensure the smooth diffusion of Pb. Finally, the effect of coexisting cation and anion experiment and the cyclic regeneration experiment indicated that CEA-2 had prominent stability and reusability for Pb adsorption.