Silicate Minerals Research Articles

Insights on the origin of oldhamite in enstatite meteorites from Ca stable isotopes

In order to understand the origin of oldhamite (CaS) in enstatite meteorites, we report Ca isotopic compositions (δ44/40Ca) of oldhamite (obtained from water leachate of bulk chondrites and aubrites and mineral separates from the Norton County aubrite) and silicate minerals from different types of enstatite chondrites and aubrite. The δ44/40Ca of the bulk enstatite chondrites range from 1.05 ‰ to 1.24 ‰, with an average of 1.13 ± 0.12 ‰, higher than that of the estimate of the bulk silicate earth (∼0.94 ‰). Major and trace element analyses show that the water leachates of enstatite chondrites are mainly composed of oldhamite, and they take over 20.6–68.5 % Ca of the bulk meteorite Ca budget. The Ca isotope fractionation between oldhamite and residual silicate (Δ44/40Caoldhamite-silicate) for the studied enstatite chondrites is minimum (−0.44 ‰) for Abee (impact-melt breccia) and maximum (+0.16) for St.Marks (EH5). The Ca isotope fractionation between oldhamite (individual mineral grains and leachate) and silicates in Norton County varies from −0.47 ‰ to −0.31 ‰ with an average of −0.41 ‰. These Δ44/40Caoldhamite-silicate correlate well with previous theoretical calculation and suggests that the oldhamites in Norton County are in isotopic equilibrium with co-existing silicates, and therefore were formed during magmatic processes. However, in enstatite chondrites, the large variation on Δ44/40Caoldhamite-silicate and its negative correlation with metamorphic temperature reflects the redistribution and equilibration of Ca isotopes during metamorphism. The variable Δ44/40Caoldhamite-silicate found in unequilibrated chondrites reflect kinetic Ca isotope fractionation between oldhamite and nebular gas and therefore is evidence for the formation of oldhamite by condensation in the solar nebula.

Hydrochemical properties and heavy metal concentrations (ecological and human risk) of lake Rukwa

This study examined lake Rukwa's hydrochemical characteristics and heavy metal levels (ecological and health hazards). Results showed that the pH ranged from 8.83 to8.95, EC ranged from 1470 to 1572.22 µS/cm, and TDS ranged from 1053.04 to 1262.63 Mg/l. The findings revealed that lake Rukwa is characterized by Na-K-HCO3 water chemical type. Gibb's diagram revealed that rock weathering and evaporation regulate water's chemical composition. The calcite and sepiolite precipitation enriches the water with Na-CO3-SO4-Cl. The study suggests silicate mineral weathering, rock-water interactions, direct ion exchange, and secondary mineral precipitation govern the geochemical evolution of lake Rukwa. The results also revealed that 30% of samples had moderate ecological risk (30 < RI < 60), whereas 70% had severe risk (60 < RI < 120). The oral hazard quotient (HQ) values for lead (Pb) in children were significantly higher (HQ > 1) at all locations, indicating a potential health risk. However, the dermal HQ values were found to be within acceptable levels. Most sites had acceptable Hazard Index (HI) values, except for Pb in children and adults. In Monte Carlo simulations, heavy metal HQ values were below standard limits, except for oral Pb exposure, which exceeded 1 for adults (7.29E-04) and children (2.79E-03). The average CR values for oral and dermal Pb in adults (7.29E-04, 3.47E-04) and children (2.79E-03, 1.02E-03) exceeded 1.0E-04, suggesting carcinogenic potential. These findings highlight significant oral and dermal carcinogenic hazards from Pb exposure to lake Rukwa and the necessity for effective comprehensive measures to mitigate these risks.

Synthesis and Crystal Structures of Two Crystalline Silicic Acids: Hydrated H-Apophyllite, H16Si16O40 • 8–10 H2O and H-Carletonite, H32Si64O144

Hydrated H-Apophyllite (HH-Apo) and H-carletonite (H-Car) were synthesized at 0 °C by leaching an apophyllite and a carletonite single crystal in a large surplus of 1.2 molar hydrochloric acid. The XRD powder patterns of HH-Apo and H-Car were indexed with space group symmetries of P4/ncc and I4/mcm and lattice parameters of a = 8.4872(2) Å, c = 16.8684(8) Å and a = 13.8972(3) Å, c = 20.4677(21) Å, respectively. The crystal structures were solved based on model building of the structures of the precursors and a physico-chemical characterization. Rietveld structure refinements confirmed the structure models. HH-Apo and H-Car are among the very few crystalline silicic acids whose structures have been determined and confirmed based on a structure refinement. The structure of HH-Apo contains thin silicate monolayers that can be regarded as constructed by rings of interconnected [SiO3OH] tetrahedra which form a puckered silicate layer. A sheet of water molecules is intercalated between the silicate layers. There are no direct hydrogen bonds between the silanol groups, but there are hydrogen bonds of different strengths between the terminal O atoms of the silicate layers and the intercalated water molecules. The 1H MAS NMR spectrum presents a strong signal at 4.9 ppm related to the aforementioned bonds and interactions between the water molecules, as well as a small signal at 22.5 ppm corresponding to an extremely strong hydrogen bond with d(O...O) ≈ 2.2 Å. The structure of H-Car is free of structural water and consists exclusively of microporous silicate double-layers with 4-connected [SiO4] and 3-connected [SiO3OH] tetrahedra in a ratio of 1:1 and a thickness of 9.2 Å. Neighboring layers are connected to each other by medium–strong hydrogen bonds with O...O distances of 2.56 Å. The structure of HH-Apo decays within several hours while H-Car is stable. A topotactic condensation reaction applied to H-Car forms an irregularly condensed silicate which still contains the layers in a distorted form as building blocks.

Geochemical indications of hydrothermal fluid through sediments within the Geolin Mounds and Mienhua Volcano hydrothermal fields, southernmost Okinawa Trough

This study focused on the chemistry of sedimentary pore fluids to clarify hydrothermal fluid migrating within sediments at the Geolin Mounds (GLM) and Mienhua Volcano (MHV) hydrothermal fields, southernmost Okinawa Trough, where are characterized by covering of thick sediment. The significant downward decrease in Mg2+ (low to 23.3 mmol L−1) and concurrent increase in Li+ (up to 2,269 μmol L−1) in sedimentary pore fluids implied a substantial influence of hydrothermal fluid, which might be associated with high-temperature (>350 °C) rock/sediment-fluid interaction. The best fitting of the 1-D advection-diffusion equation to pore-fluid Cl−, Mg2+, and Li+ concentrations further evidenced the upward hydrothermal through sediments with rates of 0.13 ∼ 124 cm yr−1. The apparently Cl-depleted and slightly Cl-enriched pore fluids in the GLM and MHV hydrothermal fields supported the occurrence of subseafloor phase separation and classified their hydrothermal fluids into vapor-rich and brine-rich phases, respectively. The low pH values (pH = 5.67 ∼ 6.21) with downward increasing trends of pore-fluid dissolved inorganic carbon (DIC, up to 60 mmol L−1) and its heavy isotopic compositions (δ13CDIC = +2.5 ∼ +7.0 ‰) inferred in-situ liquid CO2-impregnated sedimentary circumstance in the GLM and MHV hydrothermal fields. This sedimentary environment, as demonstrated, enhanced the chemical weathering of silicate and carbonate minerals, resulting in the elevated concentrations of Ca2+ and K+ in pore fluids. It highlights the impact of acidic and in-situ CO2-saturated fluids within sediments on geochemical alterations of bulk solids/sediments and interstitial fluids.

Speciation Characterization and Environmental Stability of Arsenic in Arsenic-Containing Copper Slag Tailing.

The increasing presence of arsenic-containing impurities within Cu ores can adversely affect the smelting process and aggravate the environmental impact of slag tailing. This study investigates the geochemical, mineralogical, and chemical speciation characteristics to better understand the association and environmental stability of metal(loid)s in copper slag tailing. The results indicate that the predominant chemical compositions of the selected slag tailing are Fe2O3 (54.8%) and SiO2 (28.1%). These tailings exhibit potential for multi-elemental contamination due to elevated concentrations of environmentally sensitive elements. Mineral phases identified within the slag tailings include silicate (fayalite), oxides (magnetite and hematite), and sulfides (galena, sphalerite, arsenopyrite, and chalcopyrite). The consistent presence of silicate, iron, arsenic, and oxygen in the elemental distribution suggests the existence of arsenic within silicate minerals in the form of Si-Fe-As-O phases. Additionally, arsenic shows association with sulfide minerals and oxides. The percentages of arsenite (As(III)) and arsenate (As(V)) within the selected slag tailings are 59.4% and 40.6%, respectively. While the slag tailings are deemed non-hazardous due to the minimal amounts of toxic elements in leachates, proper disposal measures should be taken due to the elevated carbonate-bound levels of As and Cu present in these tailings.

Effects of transient flow conditions on colloid-facilitated release of decabromodiphenyl ether: Implications for contaminant mobility at e-waste recycling sites

Polybrominated diphenyl ethers (PBDEs) are ubiquitous contaminants, especially in the soil and groundwater of contaminated sites and landfills. Notably, 2,2′,3,3′,4,4′,5,5′,6,6′-decabromodiphenyl ether (BDE-209), one of the most frequently and abundantly detected PBDE congeners in the environment, has recently been designated as a new pollutant subject to rigorous control in China. Colloid-facilitated transport is a key mechanism for the release of PBDEs from surface soils and their migration in the aquifer, but the effects of hydrodynamic conditions, particularly transient flow, on colloid-facilitated release of PBDEs are not well understood. Herein, we examined the effects of typical transient flow conditions on the release characteristics of colloids and BDE-209 from surface soil collected from an e-waste recycling site by undisturbed soil core leaching tests involving multiple dry–wet cycles (with different drying durations) and freeze–thaw cycles. We observed significant positive correlations between BDE-209 and colloid concentrations in the leachate in both the dry–wet and freeze–thaw leaching experiments, highlighting the critical role of colloids in facilitating BDE-209 release. However, colloids mobilized during the dry–wet cycles contained higher contents of BDE-209 than those in the freeze–thaw cycle tests, and the difference was primarily due to the more intensive disintegration of soil aggregates and elution of newly formed inorganic colloidal particles (mainly primary silicate minerals such as quartz and albite) with low BDE-209 content during the freeze–thaw process. These findings underscore the necessity of considering transient flow conditions when assessing the fate and risks of PBDEs at contaminated sites.

Surface-Modified Wheat Straw for the Production of Cement-Free Geopolymer Composite: Effects of Wheat Variety and Pre-Treatment Method

The development of new composite materials with specific properties and reduced environmental pollution can be achieved by the incorporation of agricultural residues, whose morphology is strongly affected by their variety and growing conditions. Herein, the functional properties of a cement-free geopolymer composite reinforced with straw from two wheat varieties (Ada and Malibu) were investigated through different straw pre-treatment methods and their surface modification with silane coupling agents. The characterization of the wheat surface and the geopolymer composites involved SEM-EDS, TGA, FTIR, and gas physisorption analysis methods supplemented with mechanical strength and moisture ingress measurements. Mild (23 °C) and severe (100 °C) physical pre-treatment methods with chemical soaking in 7.3 M isopropanol solution were applied on wheat straw. Tetraethoxysilane (TEOS) with octadecylamine was employed for chemical surface modification. The set of geopolymer compositions was prepared with untreated, pre-treated, and modified straws. The results revealed the hot pre-treatment method caused a higher degradation of siliceous layers of straw, especially in the Ada variety. The modification with TEOS resulted in irregular silane coating formation regardless of the wheat variety and pre-treatment method. Despite good interfacial bonding of the modified straw with the geopolymer matrix, the mechanical strength of the composites was reduced, although the resistance to water ingress slightly increased. Comparing both varieties, Ada wheat showed better performance than Malibu.

Spatial patterns and controlling factors of radon concentration in Quaternary alluvial-lacustrine aquifer systems

Radon (222Rn), naturally occurring in subsurface environments, is a significant environmental carcinogen when consumed via 222Rn-enriched groundwater and acts as a valuable geochemical tracer of the interaction between groundwater and surface water. Identifying the spatial patterns and influential factors of 222Rn in groundwater is therefore critical. However, there is a scarcity of specific studies on alluvial-lacustrine plains. In this study, 170 groundwater samples were collected to analyze the spatial patterns and controlling factors of 222Rn in the central Yangtze River plain, a typical alluvial-lacustrine plain. Through correlation and principal component analyses, as well as a random forest model (RF), it was determined that the groundwater 222Rn concentration was affected by several factors, including the hydrogeochemical environment, its associated water-rock interactions, the provenance of aquifer sediments, their mineral composition, and spatial distances from bedrock. Specifically, a thinner layer of Quaternary strata closer to the bedrock, combined with a less reducing hydrogeochemical setting and shorter-term water-rock interactions, along with a higher presence of silicate minerals in the aquifer sediments, promoted the accumulation of 222Rn in groundwater. An RF model was employed to predict the spatial distribution of the 222Rn concentration in the alluvial-lacustrine aquifer, revealing elevated groundwater 222Rn concentrations around local uplifts within the plain, at its edges, and near shallow-buried faults. The insights gained from this study can be applied to similar alluvial-lacustrine plains globally.

Synthesis and Crystallization Mechanism for SAPO-34 Zeolite Derived from Magadiite.

In this work, we explored the hydrothermal synthesize and crystallization process of SAPO-34 zeolites from two-dimensional layered silicate magadiite by using tetraethylammonium hydroxide (TEAOH) as a templating agent. Comprehensive characterization was conducted by XRD, SEM, FTIR, Raman, and BET. Time-resolved PXRD analysis revealed that SAPO-34 zeolite exhibited a steep growth curve when the crystallization time was 30 h, and the crystallinity reached 98.65 % at 48 h. Specifically, the disruption of the magadiite layer exposed charged silanol groups on the surface, fostering an affinity for AlO4 and PO4 species, thereby initiating the nucleation process. Under the guidance of TEAOH, these nucleation sites transformed into SAPO-34 nuclei, gradually advancing towards crystallization. FTIR and Raman analyses affirmed the presence of 6Rs, followed by D6R and 4Rs SBUs, along with the characteristic CHA structure. Combined with 29Si NMR established that disaggregated silicate minerals served as zeolite synthesis "seeds", enhancing nucleation sites and overall crystallization efficiency.

Epitaxial growth of Nd2O3 layers on virtual SiGe substrates on Si(111)

This study explores the growth and structural characteristics of Nd2O3 layers on virtual germanium-rich SiGe substrates on Si(111). We focus on the emergence of the hexagonal phase depending on the stoichiometry of the virtual substrate. X-ray diffraction measurements reveal a hexagonal phase when Nd2O3 is grown directly on Si(111), while growth on Ge leads to a cubic oxide structure. On SiGe layers, the growth of the oxide results in a mixed phase containing hexagonal and cubic regions, regardless of the Ge content. The cubic structure grown on virtual Ge substrates exhibits strong tensile strain, while layers grown on SiGe layers show no strain. In situ growth control via electron diffraction shows a dependence of the oxide structure of the surface reconstruction of the virtual substrate. Growth on a 7×7 reconstruction leads to hexagonal parts on Si-based substrates, while growth on c(2×8) results in cubic oxide growth on Ge. Furthermore, oxide layers grown on virtual SiGe substrates form an interfacial silicate layer. The thickness of the interfacial layer is influenced by the Si content and the structure of the oxide layer enabling oxygen diffusion pathways.

Genetic mechanism of geothermal water in the sandstone reservoir of western Sichuan, SW China: Evidence from hydrochemistry and δD − δ18O isotopes

Geothermal energy is the vital clean and renewable energy in the world. In China, most of high−temperature sedimentary − type geothermal waters are developed in western Sichuan, such as geothermal springs in the Litang county. In this study, hydrochemistry and δD − δ18O isotopes were investigated to clarify the genetic mechanism of high−temperature sedimentary − type geothermal waters in the Litang county. The self-organized map and Piper diagram showed three hydrochemical types of geothermal waters: (1) HCO3 − SO4 − Na, (2) HCO3 − Na with low Cl− concentration, (3) HCO3 − Na with high Cl− concentration. Cluster 1 geothermal water of Na − HCO3 − SO4 was dominated by dissolution of silicate and sulfate minerals. Cluster 2 geothermal water of HCO3 − Na with low Cl− concentration was affected by dissolution of silicate and CO2 degassing and mixed by large amounts of shallow cold water. Cluster 3 geothermal water of HCO3 − Na with high Cl− concentration was affected by dissolution of sandstone silicate and CO2 degassing and mixed by less shallow cold water. The recharge elevation of geothermal water in Litang ranges from 4799 to 4972 m, with an average of 4915 m. This suggests that the recharge sources of geothermal water are snow melt water and magmatic water. Cluster 3 geothermal water displayed the largest contribution of magmatic water. The temperature of HCO3 − SO4 − Na geothermal water after mixing is 92−102 °C, with an average of 97 °C; the initial temperature of HCO3 − Na with low Cl− geothermal water is 60−72 °C, with an average of 65 °C; the initial temperature of HCO3 − Na with high Cl− geothermal water is 74−91 °C, with an average of 81 °C. The temperature of geothermal water after mixing is Class 1 > Class 3 > Class 2. From the perspective of reservoir temperature, the Class 3 of geothermal water had the highest values, followed by Class 1 and Class 2 of geothermal water. From the perspective of cold − water mixing ratio, Class 2 and Class 3 of geothermal water had a similar mixing ratio, slightly higher than that of Class 1 of geothermal water. Therefore, the class 3 geothermal water with HCO3 − Na with high Cl− concentration possess the great potential for exploitation.

The effects of local variations in conditions on carbon storage and release in the continental mantle.

Recent advances indicate that the amount of carbon released by gradual degassing from the mantle needs to be revised upwards, whereas the carbon supplied by plumes may have been overestimated in the past. Variations in rock types and oxidation state may be very local and exert strong influences on carbon storage and release mechanisms. Deep subduction may be prevented by diapirism in thick sedimentary packages, whereas carbonates in thinner sequences may be subducted. Carbonates stored in the mantle transition zone will melt when they heat up, recognized by coupled stable isotope systems (e.g. Mg, Zn, Ca). There is no single 'mantle oxygen fugacity', particularly in the thermal boundary layer (TBL) and lowermost lithosphere, where very local mixtures of rock types coexist. Carbonate-rich melts from either subduction or melting of the uppermost asthenosphere trap carbon by redox freezing or as carbonate-rich dykes in this zone. Deeply derived, reduced melts may form further diamond reservoirs, recognized as polycrystalline diamonds associated with websteritic silicate minerals. Carbon is released by either edge-driven convection, which tears sections of the TBL and lower lithosphere down so that they melt by a mixture of heating and oxidation, or by lateral advection of solids beneath rifts. Both mechanisms operate at steps in lithosphere thickness and result in carbonate-rich melts, explaining the spatial association of craton edges and carbonate-rich magmatism. High-pressure experiments on individual rock types, and increasingly on reactions between rocks and melts, are fine-tuning our understanding of processes and turning up unexpected results that are not seen in studies of single rocks. Future research should concentrate on elucidating local variations and integrating these with the interpretation of geophysical signals. Global concepts such as average sediment compositions and a uniform mantle oxidation state are not appropriate for small-scale processes; an increased focus on local variations will help to refine carbon budget models.

Theory behind an innovative non-disassembly repair technology for assembles in marine, railway, and motor transport, as well as industrial equipment in the Arctic

Tribological compositions on the basis of layered silicates and, specifically, serpentine have been known for over thirty years. Their effectiveness is confirmed by successful application in many industries, in agriculture, on sea and river vessels, on railroads, in mining equipment, on passenger and goods vehicles, as well as by tests conducted at many leading industrial research institutes and universities of the Russian agro-industrial complex. The article presents the theoretical aspects of the technology for applying friction geomodifiers related to innovative nanotechnologies, which enable a significant improvement in the operating characteristics of new, as well as worn-out, expensive equipment containing friction assemblies.The use of the proposed technology for restoring worn-out equipment components under harsh climatic conditions of the Arctic seems particularly feasible and economically justified.

Interpretation of Geological Features and Volcanic Activity in the Tsiolkovsky Region of the Moon

The Tsiolkovsky crater is located on the farside of the Moon. It formed in the late Imbrian epoch and was filled with a large area of mare basalts. Multisource remote sensing data are used to interpret the geological features of the Tsiolkovsky area. Compared with previous studies, new remote sensing data and a chronological model based on crater size–frequency distribution are used to further refine the stratigraphic units and determine the absolute ages of the mare basalt units. The evolution of volcanic activity in this crater is discussed. The results are as follows: Abundances of major elements, Th, and silicate minerals suggest that the mare basalt in the crater floor is not a uniform unit but rather nine units with different compositions. The nine basalt units are divided into two episodes of volcanic activity: The first occurred at 3.5–3.7 Ga, when highly evolved lava erupted at the crater floor at a large scale; the second occurred at ~3.4 Ga, when a small area of more primitive lava extended to the northern portion of the crater floor.

Nanoclay Hydrogel Microspheres with a Sandwich-Like Structure for Complex Tissue Infection Treatment.

Addressing complex tissue infections remains a challenging task because of the lack of effective means, and the limitations of traditional bioantimicrobial materials in single-application scenarios hinder their utility for complex infection sites. Hence, the development of a bioantimicrobial material with broad applicability and potent bactericidal activity is necessary to treat such infections. In this study, a layered lithium magnesium silicate nanoclay (LMS) is used to construct a nanobactericidal platform. This platform exhibits a sandwich-like structure, which is achieved through copper ion modification using a dopamine-mediated metallophenolic network. Moreover, the nanoclay is encapsulated within gelatin methacryloyl (GelMA) hydrogel microspheres for the treatment of complex tissue infections. The results demonstrate that the sandwich-like micro- and nanobactericidal hydrogel microspheres effectively eradicated Staphylococcus aureus (S. aureus) while exhibiting excellent biocompatibility with bone marrow-derived mesenchymal stem cells (BMSCs) and human umbilical vein endothelial cells (HUVECs). Furthermore, the hydrogel microspheres upregulated the expression levels of osteogenic differentiation and angiogenesis-related genes in these cells. In vivo experiments validated the efficacy of sandwich-like micro- and nanobactericidal hydrogel microspheres when injected into deep infected tissues, effectively eliminating bacteria and promoting robust vascular regeneration and tissue repair. Therefore, these innovative sandwich-like micro- and nanobacteriostatic hydrogel microspheres show great potential for treating complex tissue infections.

The origin of high salinity and hydrogeochemical characteristics of groundwater in semi-arid area of the Linta Basin, Southwestern Madagascar

The Linta Basin, located in the Southwestern Madagascar, is a semi-arid area where groundwater in fractured media bedrock aquifer constitutes the main source of water supply. In the last two decades, highly mineralized groundwater was identified in this area; however, the origin of the salinity was not clear. The purpose of the study was to clarify the origin of salinity and to identify hotspots with groundwater unsuitable for water supply. Groundwater quality in this basin was investigated by hydrogeochemical and isotopic methods accompanied by mineralogical study. In total, 32 groundwater samples were collected and analyzed. The results showed that groundwater temperature varied from 25.2 °C to 31.7 °C. Values of pH and TDS varied from 6.55 to 8.24 and 221 to 5612 mg/L, respectively. The aquifer, which is mainly fractured, showed 7 groundwater types, namely Mg–HCO3,Na–HCO3 and also Na–C1, Mg–Cl, Na–Cl–HCO3, Mg–Cl–HCO3-, and Ca–Mg–HCO3. Two groups of variables have been identified by factor analysis; the factor F1 comprises EC, Ca2+, Mg2+, SO42−, and Cl− whereas the factor F2 comprises HCO3−, K+, and Na+, and they were interpreted in terms of hydrogeochemical processes. Values of saturation indices (SI) for carbonate minerals were generally positive, indicating their possible precipitation. Based on the Gibbs diagram and factor analysis, groundwater mineralization is affected by water-rock interactions and evaporation, respectively. The important role of evaporation is confirmed by enrichment of stable isotopes with δ18O values up to 1.2 ‰. Processes such as base ionic exchange process and reverse ionic exchange process may also be important locally. The main origin of groundwater mineralization is the hydrolysis of silicate minerals such as feldspars and micas coupled with evaporation. In several wells, salinity is too high for water supply and nitrate concentration is above the WHO limit for drinking water. Results of the study highlighted groundwater chemistry formation processes and are applicable in other African countries with bedrock aquifers.

Crystal chemistry and molar volume of potassic-chloro-hastingsite

Abstract. Several geological processes such as crustal and mantle metasomatism, high-grade metamorphism, and the formation of ore deposits involve the exchange of halogens, especially chlorine, between silicate minerals and fluids. It is well established that the presence of octahedral iron is vital to the process of Cl incorporation into amphiboles. However, other compositional controls on Cl incorporation, such as the effect of TAl, ANa, AK, and A-site occupancy are not as well constrained. This study reports on the compositional and structural relationships amongst a suite of 25 synthetic calcium amphiboles with a diverse range of Cl contents (0–1.68 atoms per formula unit (apfu)). Most amphiboles were synthesized along the potassic-hastingsite–potassic-chloro-hastingsite join (KCa2(Fe4Fe3+)(Al2Si6)O22(OH,Cl)2). Additional work involved substitution of Na for K, variable Al content, and substitution of Mg for Fe2+ in the bulk composition to explore these compositional effects on Cl incorporation. The relationship between pressure and the Cl content of amphiboles was also explored over the pressure range 0.3–2.0 GPa. Otherwise, synthesis conditions were 700 °C and 0.3 GPa with fO2 near Ni–NiO. Iron (II) chloride was used as the source of Cl. Some experiments used variably concentrated FeCl2 brines (0–100 molal), while others were nominally anhydrous, containing only the water absorbed by the hygroscopic FeCl2. All amphiboles were characterized by Rietveld refinements of powder X-ray diffraction patterns, electron microprobe analysis, and Mössbauer spectroscopy, the latter to determine Fe3+ fraction. This study finds a positive relationship between pressure and the Cl content of the amphibole. Both Fe2+ and Fe3+ are positively correlated with Cl among amphiboles with variable Fe#, but the correlation is poor to nonexistent for Mg-free amphiboles. Results indicate that the substitution of CFe2+,3+ for CMg and CFe2+,3+ for CAl facilitate Cl incorporation, with the former having a larger effect. The A-site occupancy is positively correlated with Cl in all amphiboles except those synthesized in dilute FeCl2 brines (≤ 6 m), which are negatively correlated. No correlation is observed between the Cl content of the amphibole and either the species of A cation (K vs. Na) or TAl. The composition vs. unit cell parameter data were analyzed using multivariate linear regression to better understand the process of Cl incorporation and to predict the molar volume of endmember chloro-amphiboles. The regression indicates an expansion of 0.181 Å (0.99 %) and 0.048 Å (0.90 %) along the b and c edges respectively, a reduction in β by 0.76° (0.72 %), and a contraction of 0.060 Å (0.59 %) along a when fully substituting Cl for OH in potassic-hastingsite. The multivariate linear regression equations allow the prediction of molar volumes for select endmember chloro-amphiboles, such as potassic-chloro-hastingsite = 964.63 ± 1.29 Å3 or 290.5 ± 0.4 cm3 mol−1.

Sodium adsorption on nanometer-thick TiO2 channel thin-film transistors for enhanced drain currents

Sodium adsorption on nanometer-thick-TiO2-channel thin-film transistors (TFTs) are examined for enhancing the drain current. In the TFTs, the channel thickness of TiO2 is set as thin as ∼16 nm. The TiO2 film is deposited by atomic layer deposition using plasma excited humified Ar, followed by crystallization into the anatase phase by thermal annealing at 500 °C in air. The gate oxide is a 300 nm thick SiO2 film, which is grown on a highly doped n+ Si substrate. The n+ Si substrate is used as the gate electrode. The drain and source electrodes of Ti are deposited by an electron beam evaporation at room temperature. The TiO2 channel is covered with multiple layers of aluminum silicate and SiO2 films to enhance the Na sorptivity. The multiple films consist of combinations of 1 nm thick SiO2 and 0.16 nm thick aluminum silicate. The channel length and width are 60 and 1000 μm, respectively. The TFT without the Na adsorption exhibits a field effect mobility of ∼0.5 cm2/V s, where the drain current is recorded around 30 μA with a gate voltage of 10 V. With immersion of the TFT in a 10 mM NaCl solution, the drain current is enhanced to the order of mA. The simulation with an equivalent circuit with source and drain resistances suggests that the field effect mobility is enhanced to ∼30 cm2/V s with the adsorption of Na. In this paper, we discuss the operation mechanism of the Na adsorbed TiO2 TFT and its applicability as TFT-based high current switch devices and sensors.

Geochemical Weathering Variability in High Latitude Watersheds of the Gulf of Alaska

AbstractHigh latitude regions across the globe are undergoing severe modifications due to changing climate. A high latitude region of concern is the Gulf of Alaska (GoA), where these changes in hydroclimate undoubtedly affect the hydrogeochemistry of freshwater discharging to the nearshore ecosystems of the region. To fill the knowledge gap of our understanding of freshwater stream geochemistry with the GoA, we compile stream water chemistry data from 162 stream sites across the region. With an inverse model, we estimate fractional contributions to solute fluxes from weathering of silicate, carbonate, and sulfide minerals, and precipitation. We assess weathering rates across the region and compare them against global river yields. The median fractional contribution of carbonate weathering to total weathering products is 78% across all stream sites; however, there are several streams where silicate weathering is a dominant source of solutes. Weathering by sulfuric acid is elevated in glacierized watersheds. Finally, cation weathering rates are lower in GoA streams compared to the world's largest rivers; however, weathering rates are similar when compared to a global dataset of glacier fed streams. We suggest that hydrologic changes driven by glacier ice loss and increased precipitation will alter river water quality and chemical weathering regimes such that silicate weathering may become a more important source of solutes and sulfide oxidation may decrease. This contribution provides a platform to build from for future investigations into changes to stream water chemistry in the region and other high latitude watersheds.

Mechanisms controlling albite dissolution/precipitation kinetics as a function of chemical affinity: New insights from experiments in 29Si spiked solutions at 150 and 180 °C

Knowledge of the rates of dissolution of rock-forming minerals close to equilibrium and their dependence on ΔGr, the Gibbs free energy of reaction, is essential for describing the temporal and spatial evolution of many environmental and engineering processes involving solid/fluid interactions. In the present study we used the isotope-doping method to quantify albite forward and net dissolution rates. Batch experiments were performed at 150, 180 °C and pH = 9 at near equilibrium and equilibrium conditions (-25 ≤ ΔGr ≤ + 8.2 kJ/mol) in 29Si spiked solutions which were undersaturated with the secondary Al-Si solid phases likely to precipitate.The forward dissolution rates normalized to the initial BET surface area were found to decrease continuously and monotonically with increasing time and ΔGr, achieving values 1.3 to 2.4 orders of magnitude lower at chemical equilibrium than initial far from equilibrium values, with the highest rate decrease for the highest solid to fluid ratio. These rate drops were accompanied by an increase in BET specific surface areas associated with the formation of widespread dissolution features. A decrease of albite forward dissolution rate together with an increase of its BET surface area was also observed as a function of reaction time at far from equilibrium conditions (ΔGr ≤ − 65 kJ/mol). These observations are consistent with a continuous decrease with time and increasing ΔGr of albite effective surface area linked to the formation of unreactive negative crystal facets, in addition to etch pits stopping nucleating above a critical value of ΔGr. Thus, the observed decrease in albite dissolution rate as equilibrium is approached is not linked primarily to the increase in the contribution of the backward reaction but rather to the decrease of the forward reaction rate in conjunction with the decrease in the density of reactive sites at the mineral surface.The results of this study show that the characterization of the effective surface area and its evolution with reaction time and chemical affinity is crucial to deriving robust dissolution rates of well-crystallized minerals like feldspars. Dissolution experiments in 29Si spiked solutions of samples with different history and well-characterized effective surface area and surface morphology should help to better quantify the rate laws controlling silicate minerals weathering.