Silicate Composition Research Articles

Nutrient-doped synthetic silicates for enhanced weathering, remineralization and fertilization on agricultural lands of global cold regions- A perspective on the research ahead.

There is now a dire demand for negative emissions technologies (which sequester CO2 from the atmosphere) that can be rapidly deployed, are scalable, and are demonstrably safe and effective. Enhanced weathering of silicate minerals has demonstrated a significant potential for CO2 capture and sequestration by the formation of pedogenic carbonates in soils, subsoils, and sediments. This technique has also been shown to deliver fruitful results in terms of improving soil health, and in turn plant health, through remineralization. The silicate minerals that possess the highest weathering rates (e.g., wollastonite), are relatively rare in nature, whereas the abundant ones (e.g., anorthite and forsterite) have a slower pace of weathering, especially in colder and drier climates such as found in the extensive agricultural lands of Western Canada and the Western United States. Herein, we offer a perspective on the opportunities for computational studies targeting atomic-scale interaction of CO2 with silicates and synthesis of fast-weathering silicates (such as larnite and bredigite), whose composition can be tuned to also support soil fertilization and remineralization, and whose production must be integrated with green and carbon-neutral technologies to ensure net-negative life cycle emissions.

Orange waste Biochar-Magnesium Silicate (OBMS) composite for enhanced removal of U(VI) ions from aqueous solutions

The removal of toxic radioactive pollutants from water sources for further disposal and treatment is a critical issue. Development of an effective adsorbent with high adsorption capacity and stability for the adsorption of hexavalent uranium, U(VI) ions is interesting research task. In this study, orange waste biochar‑magnesium silicate (OBMS) composite was prepared by simple hydrothermal method and utilized for U(VI) ions adsorption removal from aqueous solution. The successfully synthesized OBMS composite consists of graphitic carbon biochar and interconnected magnesium silicate nanosheets exhibiting 73.9 m2/g surface area with H3 type hysterias loop suggests mesoporous texture having stacked and agglomerated magnesium silicate layers covered by biochar. The prepared composite was used to study the influence of pH, U(VI) ion concentration, mass of adsorbent, presence of other cations and determination of thermodynamic functions. It was observed that OBMS composite showed high adsorption capacity (Langmuir adsorption capacity of 352.6 mg/g at 298 K, pH 4) irrespective of presence of other cations. A series of batch experiments and characterization results revealed that the superior adsorption performance of the composite is due to interaction between U(VI) ions and functional groups presented on the OBMS composite surface. The observed results suggesting the interaction between U(VI) ions OBMS surface functional groups such as CC, COH, CO, MgOSi and Mg(OH)2 is playing a key role in removal of U(VI) ions from aqueous solution. This low-cost and easily synthesized absorbent has a great potential for use in the remediation of radioactive U (VI) ions in aquatic environments.

Study of the Interaction of Cement-Based Materials for 3D Printing with Fly Ash and Superabsorbent Polymers

The use of superabsorbent polymers (SAP) in construction is a relatively new trend, and not a completely explored area. However, SAP itself has been on the market for over 80 years. SAPs have a cross-linked three-dimensional structure, thanks to which they have the unique ability to absorb extreme amounts of water, up to a hundred times their weight. By using this property, it is possible to prevent water losses, which is important at the time of maturation in cementitious building materials. When there is a lack of water needed for hydration processes, the physical and mechanical properties deteriorate. The subject of this article is to determine the possible positive effect of the presence of SAP in the cement matrix in order to optimize the parameters of silicate composites for 3D printing. For this purpose, a special methodology was compiled consisting of tests through which it is possible to assess the suitability of the tested mixtures for 3D printing. This methodology consists of determining consistency, volumetric weight, ultrasonic analysis, buildability, X-ray diffraction, flexural tensile and compressive strength. For determining of buildability and ultrasonic analysis new methodologies were created in this research in order to be suitable for the 3D printing materials. Last but not least, efforts are also being made to increase the incorporation of secondary raw material (fly ash) in order to reduce the environmental impact of industrial production and, conversely, to increase its sustainability while maintaining or improving the mechanical–physical parameters of building materials. From the results presented in this paper it is apparent, that created methodology is efficient for determining properties of 3D printable mixtures. SAPs also significantly influenced properties of these mixtures. Mainly buildability and flexural tensile strength (by up to 30%) were increased and volumetric weight was decreased (by up to 5%).

Morphology Analysis of Friction Surfaces of Composites Based on PTFE and Layered Silicates.

In the present study, the tribological behavior of polytetrafluoroethylene (PTFE) composites filled with natural layered silicates (LS) was investigated. The change in the morphology of the friction surface of composites depending on the content and chemical composition of layered silicates has been shown. The friction surface of PTFE composites with layered silicates was investigated by scanning electron microscopy (SEM). The formation on the friction surface of a special layer with a structure different from the bulk of the polymer, which is formed from particles of fillers and wear products, has been established. The thickness of this layer is independent of the content of layered silicates in the polymer. It was indicated that wear debris of PTFE composites was assembled during friction and uniformly cover the friction surface layer by layer, thereby forming a protective layer.

Examining phase separation and crystallization in glasses with X-ray nano-computed tomography

X-ray nano-computed tomography (nano-CT) is a powerful technique to characterize and visualize 3 dimensional (3D) phenomena in complex glasses at the nanoscale. This technique can offer a unique opportunity to explore the intricate morphology of multicomponent glass and glass-ceramic samples, due to its low X-ray energy and high spatial resolution (down to 50 nm). In the current demonstration paper, nano-CT provided insight into crystallization and phase separation, as well as a variety of other phenomena, including corrosion, fracture, and porosity. At scales ranging from 100 to 20 μm, the microstructures of phase separation in borosilicate, complex silicate, and chalcogenide glass compositions were examined. In addition, crystallites present in simulant nuclear waste glasses, volcanic glasses, and other related samples were explored. Nano-CT analysis can add to the understanding of (1) the formation processes, (2) distributions, interactions, and compositions of phases, and (3) the mechanisms, structures, and growth of crystallization and phase separation. Nano-CT offers wide potential in the field of glass science, especially when (1) common characterization methods are insufficient, (2) simple sample preparation is required, (3) 3D rendering is needed, or (4) compelling images of small, complex features are desired.

In-situ synthesis of duster-like hollow mesoporous copper silicate composites for high-efficiency adsorption of aflatoxin B1 from water

Aflatoxin B1 (AFB1) is one of the pollutants widely distributed in wastewater, which easily causes serious harm to human health and ecosystem. Mesoporous silicate materials are often used as adsorbents attributed to their well-controlled structures and high surface area. Herein, copper silicate composites (MCSCs) with novel duster-like hollow mesoporous structure were synthesized in situ on an acid-etched sepiolite substrate, and used as adsorbents for removal of AFB1 from water. The resultant MCSCs exhibited high specific surface area (439 m2/g), consequently exposing abundant functional groups (e.g., Si–OH, Cu–OH and Si–O–Cu), which contributed to improved adsorption performance. As expected, the MCSCs showed excellent AFB1 adsorption capacity, and the maximum adsorption capacity, obtained from the Langmuir model, was 24.99 mg/g. Analyses of the kinetic data revealed that the adsorption process of AFB1 onto MCSCs were fitted well with the pseudo-second-order and Weber-Moris intra-particle diffusion models. The FTIR and XPS analysis confirmed that the adsorption mechanisms were mainly electron donor-acceptor interaction and hydrogen bonding. These results in this work will provide valuable information for the development of green and efficient strategy for synthesizing other silicate materials, which are expected to applied as highly efficient adsorbents to remove AFB1 from wastewater.

A sulfur and halogen budget for the large magmatic system beneath Taupō volcano

The transport and degassing pathways of volatiles through large silicic magmatic systems are central to understanding geothermal fluid compositions, ore deposit genesis, and volcanic eruption dynamics and impacts. Here, we document sulfur (S), chlorine (Cl), and fluorine (F) concentrations in a range of host materials in eruptive deposits from Taupō volcano (New Zealand). Materials analysed are groundmass glass, silicic melt inclusions, and microphenocrystic apatite that equilibrated in shallow melt-dominant magma bodies; silicic melt and apatite inclusions within crystal cores inferred to be sourced from deeper crystal mush; and olivine-hosted basaltic melt inclusions from mafic enclaves that represent the most primitive feedstock magmas. Sulfur and halogen concentrations each follow distinct concentration pathways during magma differentiation in response to changing pressures, temperatures, oxygen fugacities, crystallising mineral phases, the effects of volatile saturation, and the presence of an aqueous fluid phase. Sulfur contents in the basaltic melt inclusions (~ 2000 ppm) are typical for arc-type magmas, but drop to near detection limits by dacitic compositions, reflecting pyrrhotite crystallisation at ~ 60 wt. % SiO2 during the onset of magnetite crystallisation. In contrast, Cl increases from ~ 500 ppm in basalts to ~ 2500 ppm in dacitic compositions, due to incompatibility in the crystallising phases. Fluorine contents are similar between mafic and silicic compositions (< 1200 ppm) and are primarily controlled by the onset of apatite and/or amphibole crystallisation and then destabilisation. Sulfur and Cl partition strongly into an aqueous fluid and/or vapour phase in the shallow silicic system. Sulfur contents in the rhyolite melts are low, yet the Oruanui supereruption is associated with a major sulfate peak in ice core records in Antarctica and Greenland, implying that excess S was derived from a pre-eruptive gas phase, mafic magma recharge, and/or disintegration of a hydrothermal system. We estimate that the 25.5 ka Oruanui eruption ejected > 130 Tg of S (390 Tg sulfate) and up to ~ 1800 Tg of Cl, with potentially global impacts on climate and stratospheric ozone.

Effects of different carriers for zinc oxide (ZnO) particles on microstructure of ZnO/layered silicate composite and aging resistance of composite modified asphalt

• ZnO/layered silicate composite with three different carriers is synthesized. • Adding EVMT can significantly weaken agglomeration effects of ZnO particles. • Introducing ZnO particles can enhance UV absorption ability of layered silicates. • Exfoliated phase structure is formed in ZnO/MMT or ZnO/EVMT modified asphalt. • EVMT and REC are preferable to form composite and improve asphalt aging resistance. With the use of nanocomposite synthesis operations, the produced zinc oxide/expanded vermiculite (ZnO/EVMT) composite, a combination of ZnO particles and EVMT, has ZnO particles of the weakened agglomeration effects and can comprehensively improve the resistance of asphalt to thermo-oxidative and ultraviolet (UV) aging. However, the effects of different carriers for ZnO particles on the microstructure of ZnO/layered silicate composite and aging resistance of the composite modified asphalt are still unknown. In this research, three ZnO carriers, montmorillonite (MMT), expanded vermiculite (EVMT) and rectorite (REC), were employed to support ZnO particles (named ZnO/MMT, ZnO/EVMT and ZnO/REC, respectively). Then, the microstructure of different ZnO/layered silicate composites was investigated by field emission scanning microscope (FESEM), X-ray diffractometer (XRD) and UV–visible spectrometer (UV–vis) tests. Finally, the effects of different carriers on the morphology, phase structure, storage stability, physical properties and aging resistance of ZnO/layered silicate composite modified asphalt were discussed. Results showed that with the unique layered structure and its integrity, the three carriers are feasible to synthesize ZnO/layered silicate composite, and ZnO particles are supported or embedded on the surface of layered silicate sheets and have weaker agglomeration effects. Except for ZnO/MMT composite, the other two composites have sufficient composition connection strength. The exfoliated phase structure is formed in the ZnO/MMT or ZnO/EVMT composite modified asphalt systems. Additionally, the three ZnO/layered silicate composites have good asphalt compatibility and storage stability in asphalt, especially for ZnO/REC composite. The addition of ZnO/layered silicate composites into asphalt slightly influences physical properties of asphalt. Incorporating ZnO/layered silicate composites, regardless of the types, into asphalt could comprehensively enhance the resistance of asphalt to thermo-oxidative and UV aging. Comparatively, EVMT and REC are preferable to support ZnO particles and generate ZnO/layered silicate composite and comprehensively improve the aging resistance of asphalt.

Fast self-curing α-tricalcium phosphate/β-dicalcium silicate composites beneficial for root canal sealing treatment

Objectivesα-tricalcium phosphate (α-TCP) and β-dicalcium silicate (β-C2S) have attracted much attention since these two types of self-curing Ca-phosphate and Ca-silicate are valuable biomaterials for bone defect or endodontic therapy. However, the injectable paste of their individual with high liquid/solid ratio is junior for root canal sealing due to very long self-setting time, low pH value and/or much volume shrinkage during paste-to-cement transformation. MethodsOur studies evaluated the effect of biphasic ratio, liquid/solid ratio and pH condition of aqueous medium on setting time and mechanical strength of this biphasic composite cement, and also the hydroxyapatite re-mineralization potential and anti-microleakage level of the cements with different α-TCP/β-C2S ratio were explored in vitro. A control group free of paste filler was included in the extracted teeth model. Dentine re-mineralization and microleakage degree were observed by scanning electron microscopy and microCT reconstruction analysis. ResultsIt indicated that the weak acidic solution with pH value of 6.0 may produce a significantly shorter initial setting time (from 90 min to less 20 min) and expected final setting time (<150 min) for the biphasic composite (2:1 or 1:2) in comparison with the pure β-C2S. Notably, the phasic composites exhibited limited microleakage and induced hydroxyapatite mineralization in the dentine tubules. These hydraulic pastes also produced strong alkaline feature and appreciable compressive resistance (12–18 MPa) after setting for a very short time stage. Moreover, a link between the addition of α-TCP leading to fast re-mineralization reaction was established. SignificanceOur findings suggest that the appreciable self-setting and physicochemical properties adaption to root canal sealability make α-TCP/β-C2S composites as preferential candidates for endodontic treatments.

Degradation behavior of heat-treatment silicate adhesive under special working conditions

Inorganic adhesive is widely used in the sealing and connection of electronic devices. Its insulation is highly important in the performance of installation. In this paper, the insulation resistance and tensile strength of different composite silicate samples were measured by test machines. The morphology and surface composition were analyzed by electronic microscope and energy spectrum analyzer. The results show that: In a humid environment, the resistance insulation of adhesive increases with the rising of heat treatment temperature, and decreases with the increment of wet environment. When the modulus ratio of colloidal liquid is in the range of 7.2~9.1 and the heat-treatment temperature is larger than 600°C, the effect of moisture resistant is remarkable. The tensile strength of adhesive deteriorates with the increasing of humidity. Furthermore, with ascending heat treatment temperature, the tensile strength rises when the modulus ratio of adhesive is less than 7.2, and declines when it is more than 9.1.

Modified Polymer Surfaces: Thin Films of Silicate Composites via Polycaprolactone Melt Fusion

Polymer/layered silicate composites have gained huge attention in terms of research and industrial applications. Traditional nanocomposites contain particles regularly dispersed in a polymer matrix. In this work, a strategy for the formation of a composite thin film on the surface of a polycaprolactone (PCL) matrix was developed. In addition to the polymer, the composite layer was composed of the particles of saponite (Sap) modified with alkylammonium cations and functionalized with methylene blue. The connection between the phases of modified Sap and polymer was achieved by fusing the chains of molten polymer into the Sap film. The thickness of the film of several μm was confirmed using electron microscopy and X-ray tomography. Surfaces of precursors and composite materials were analyzed in terms of structure, composition, and surface properties. The penetration of polymer chains into the silicate, thus joining the phases, was confirmed by chemometric analysis of spectral data and changes in some properties upon PCL melting. Ultimately, this study was devoted to the spectral properties and photoactivity of methylene blue present in the ternary composite films. The results provide directions for future research aimed at the development of composite materials with photosensitizing, photodisinfection, and antimicrobial surfaces.

High P-T experimental perspective on Cr isotopic fractionation during planetary core formation

Core formation may modify the stable isotopic signatures for both the mantles and cores of differentiated planetary bodies. We performed high P-T experiments with a piston-cylinder apparatus at 1 GPa and 1873-2073 K to determine the Cr isotopic fractionation factor during metal-silicate segregation. Experimental results consistently indicate that the metal phase is isotopically heavier than the coexisting silicate phase, with Δ53Crmetal-silicate up to 0.3‰ at the investigated experimental conditions. Oxygen fugacity, silicate composition, and S content in the metal phase do not have significant effects on the Cr isotopic fractionation factor. By contrast, increasing Ni content in the metal increases the Δ53Crmetal-silicate value, implying that the Ni content of the core could influence planetary isotopic signatures. We conclude that heavier Cr isotopes enter the core preferentially during planetary core formation. The δ53Cr value of the terrestrial mantle could be lowered by up to ∼0.02‰ by core formation, despite that this is within current analytical uncertainty of chondritic Cr isotopic composition. For smaller bodies such as the Moon, Mars, and Vesta, the lower core formation temperatures could potentially generate a resolvable core-mantle Cr isotopic fractionation. However, the Moon's small core size would limit the change in the Cr isotopic composition of the lunar mantle compared to chondritic. For Vesta and Mars, core formation could lower the δ53Cr values of their mantles by ∼0.01-0.02‰, which is trivial relative to the analytical uncertainty. On the other hand, core formation could increase the δ53Cr values of the cores of the parent bodies of iron meteorites by up to ∼0.2‰ at 1873 K. Therefore, the significantly heavy Cr isotopic composition (up to 2.85‰) of iron meteorites cannot be explained by equilibrium fractionation between the core and the mantle of the parent bodies of iron meteorites.

Sulfide mineralization in Sikhuran ophiolite complex, Esfandagheh, Iran: Implications from trace element composition of silicate and sulfides

The Sikhuran ophiolite complex in Esfandagheh, Kerman province, is considered one of the important chromite mining areas in southern Iran. The complex is comprised of mainly tectonized harzburgite of residual upper mantle, depleted harzburgite, chromitite, dunite, and orthopyroxenite of the transition zone, as well as upper cumulates of ultramafic-mafic rocks. Sulfide disseminations, i.e., pentlandite, chalcopyrite, chalcocite, millerite, and heazlewoodite are hosted by dunite and chromitite in the upper part of the transition zone. The abundance of Base Metal Sulfides (BMS) as interstitials of olivine shows early stage sulfur saturation in Mg-rich magmas. Low Ni contents of ubiquitous olivine indicate that Ni in the primary silicate melt is preferentially concentrated in the sulfide liquid. The high activity of Ni in the melt is evidenced by the dominance of Ni-rich pentlandite and other Ni-bearing minerals from the Sikhuran ophiolite complex. Major and trace element compositions indicate that pentlandite is the main PGE-carrier with ƩPGE up to 44 ppm. Palladium, the most abundant PGE, is partitioned into pentlandite by diffusion of Monosulfide Solid Solution (MSS). The factors affecting this mechanism include the initial concentration of Pd, low compatibility of Pd compared to IPGEs, and decreasing solubility of Pd in MSS with decreasing temperature. Generally, although no detailed studies have been conducted on the occurrence of sulfide minerals in Iran; sulfide mineralization with coarse sulfide minerals in the Sikhuran can be a new perspective for mining companies and economic geologists.

Design of multilayer cauliflower-like structure SiO2/SiC–Y2Si2O7 composite ceramics as high-efficiency electromagnetic wave absorbers

A reasonable design of the microstructure and phase composition of rare earth silicate composites can enhance their corrosion resistance and their electromagnetic (EM) properties. However, individual rare earth silicates cannot fulfill the requisites for novel EM absorption materials. Herein, we introduce SiC and SiO2 to establish novel SiO2/SiC–Y2Si2O7 composite ceramics with a multilayer cauliflower-like structure using sol-gel, pressure-free sintering, chemical vapor infiltration (CVI) and oxidation at 1100 °C (1.5 h). SiC increases the relative complex permittivity and attenuation capabilities and the SiO2 layer impedance matching mediator effectively balances the impedance matching properties. The SiO2/SiC–Y2Si2O7 composite ceramics, therefore, exhibit superior EM wave absorption properties: the reflection coefficient minimum (RCmin) is −21.5 dB, with a 3.65 mm thick covering, in the whole X band (4.2 GHz). This is due to the impedance matching, polarization loss, conductivity loss, and internal multiple reflections loss. In brief, this work provides a strategy for achieving the EM stealth characteristics of rare earth silicate materials.

Performance sensitivity analysis of natural mineral silicates filled friction composites using GD – ANN approach

Abstract Structurally dissimilar clay type silicate (tubular halloysite, platy montmorillonite, and acicular wollastonite) reinforced compression molded composites were fabricated with and without MgO. The thermo-mechanical and frictional performances of natural silicate-based friction materials were systematically evaluated with respect to the silicate and silicate-MgO free composites. The morphology and hardness of the natural silicates dominated the mechanical and tribological responses of the friction materials. The worn surface morphology revealed the influence of natural silicate on braking dynamics as evident from performance sensitivity analysis, braking load, sliding speed, and temperature. The nature of sliding-induced tribo-layers was ascertained from elemental mapping by EDX and Raman spectroscopy indicating the friction composition of tribo-layer to be influencing performance sensitivity. Under the variable operating conditions, halloysite-based friction materials showed excellent wear resistance, and wollastonite-based friction composites with MgO enhanced the friction coefficient (~0.43- 0.61) while exhibiting minimum load-speed sensitivity. The gradient descent learning algorithm based-artificial neural network (GD-ANN) with optimally tuned network architecture predicted (R2 ~ 97 %) both the tribological performance attributes (coefficient of friction and specific wear rate) of the natural silicate-filled friction composites more accurately as compared to the conventional regression analysis.

Експериментальне дослідження впливу зернистості абразиву силікатної пасти на якість поверхонь тертя

Currently, many technological methods have been developed to change the structure and properties of surface layers of metal in the desired direction or to create layers with predefined properties. The use of these methods can increase wear resistance, resistance to fatigue and other performance properties of automotive parts. One such method is grinding with abrasive compounds. Grinding technology consists in applying abrasive compositions on the surface of the part and subsequent machining using special devices.The results of experimental research of influence of granularity of abrasive of silicate paste on quality of friction surfaces are resulted in work. Silicate compositions with electrocorundum abrasive of different grain size were made for the study. In order to compare the performance of silicate paste, the existing abrasive pastes «KT» with abrasive titanium carbide abrasive of similar grain size were selected. The research was performed on a special installation, which allows to reproduce with high accuracy the process of processing the abrasive composition in the laboratory. The evaluation was based on the duration of grinding, metal removal and surface quality. Stabilization of the coefficient of friction showed the completion of the grinding process.The study confirms that with increasing grain size of the abrasive silicate composition increases the time of formation of the surface layer and the amount of metal that is removed. It is proved that the high quality of the surface after treatment with silicate composition is due to the appearance in the grinding process of amorphous silica (SiO2), which enhances the work of abrasive grains and reduces the action of the scratching abrasive. Under the action of abrasive particles, SiO2 enters the depressions of the treated surface and adheres to the surface. It is established that the productivity of grinding with silicate composition is 1.5 times higher than when treating surfaces with «KT» paste. It was found that when treating surfaces with a silicate composition with electrocorundum abrasive, the removal of metal is 1.8 times less than when treating with «KT» paste. It is proposed to assign an allowance for treatment with silicate paste from 0.035 to 0.07 mm.

Excellent corrosion resistance of FGO/Zn2SiO4 composite material in epoxy coatings

Generally, the anti-corrosion performance of the coating is improved by adding organic or inorganic anti-corrosion materials to the epoxy coating. In this paper, P-phenylenediamine-functionalized graphene oxide/zinc silicate (FGO/Zn2SiO4) composites were synthesized in situ by hydrothermal method as filler in epoxy resin. P-phenylenediamine (PPDA) acts as a spatial barrier between graphene oxide (GO) layers and improves FGO/Zn2SiO4 dispersion in the epoxy coating. The corrosion resistance of FGO/ Zn2SiO4 material is 234.4 % of GO/Zn2SiO4 material and 763.6 % of Zn2SiO4 material. Because GO/Zn2SiO4 composite has numerous oxygen-containing groups that tend to agglomerate, which results in reduced dispersion in epoxy coatings. However, FGO not only prolongs the diffusion path of corrosion ions in the coating and reduces the rate of charge transfer for electrochemical reflection, but the amino group on the PPDA provides additional cross-linking on top of the epoxy cure to improve dispersion. Utilizing the synergistic anti-corrosion effect of inorganic and organic materials, a new type of Zn2SiO4 anti-corrosion filler was designed, which significantly improved the anti-corrosion performance of Zn2SiO4 in epoxy resin coating.

16O-rich anhydrous silicates in CI chondrites: Implications for the nature and dynamics of dust in the solar accretion disk

CI chondrites have nonvolatile chemical compositions closely resembling that of the Sun’s photosphere and are thus considered to have the most primitive compositions of all known solar system materials. They have, however, experienced pervasive parent-body alteration processes that transformed their primary constituents, obscuring the nature and origin of primordial CI dust. We used in-situ quantitative microprobe and secondary ion mass spectrometry techniques to characterize the chemistry and oxygen isotopic compositions of anhydrous silicates in two sections of the CI chondrites Ivuna and Alais, which contain higher abundances of those than other CI samples. These silicates are Mg-rich olivine and low-Ca pyroxene crystals mostly occurring as aggregates within sub-mm Fe-rich clasts. Our data reveal mass-independent oxygen isotopic variations with Δ17O values ranging from −23.63 to −0.57‰, representing the first evidence of extremely 16O-rich (Δ17O < −20‰) olivine and pyroxene grains in CI chondrites. Two of these olivines are characterized by MnO/FeO ∼ 1, typical of low-iron, Mn-enriched silicates commonly observed in amoeboid olivine aggregates. Other anhydrous silicate grains have Δ17O values ranging from −6 to 0‰, probably representing chondrule fragments. Combined, these results indicate that chondrule and refractory inclusion material were incorporated into the CI parent body(ies). This conclusion is consistent with recent models showing that refractory inclusions could have formed and/or been transported at larger heliocentric distances than previously thought during the concomitant injection of material from the molecular cloud and outward extension of the disk by viscous spreading. The CI chondrules are presumably of local origin, with their isotopic systematics suggesting an affinity with the CR clan.

In Situ Hydrothermal Synthesis of Metallic Bi Self‐Deposited Bi2SiO5 with Enhanced Photocatalytic CO2 Reduction Performance

Metal‐modified nanomaterial has been regarded as an effective way to improve its photocatalytic CO2 reduction performance. Herein, metallic Bi self‐doped Bi2SiO5 composites are successfully in situ synthesized via a simple OH−‐assisted hydrothermal controllable route. The experimental results reveal that 2 mol L−1 NaOH plays two roles in the formation of Bi/Bi2SiO5 composites: 1) increasing the specific surface area through cracking the flower‐like microspheres of Bi2SiO5 with the increase of pH value, 57.92 m2 g−1 (pH = 13), 1.54 times as large as pure Bi2SiO5 (pH = 10); 2) dissolving out the different metallic Bi contents by adjusting the volume of 2 mol L−1 NaOH, achieving the optimum metallic Bi content of about 9.01%. Additionally, combined with experimental data and physicochemical characteristics, the novel mechanism of metallic Bi self‐doped bismuth silicate composites is investigated, and an interesting linear relationship between the metallic Bi with the volume of 2 mol L−1 NaOH is confirmed. The Bi/Bi2SiO5 (pH = 13) sample exhibits the highest CO2 photoreduction activity and stability to CO, more than 2.2 times that of pure Bi2SiO5 (pH = 10), which should be mainly attributed to the surface plasmonic resonance effect of metallic Bi, the strong light absorption ability, and the interfacial interaction between metallic Bi and Bi2SiO5.

Retardation Effects of Filter Mud in Molasses on Composite Silicate Cement.

The filter mud in molasses has a significant inhibitory effect on biological activity and cannot be utilised by organisms; therefore, before molasses are biotransformed, the filter mud will be separated and directly discarded in the environment. In this study, the filter mud was used as the retarder of cement concrete OPC 42.5 for the first time. It was found that when 0.2–0.8% filter mud was added to fresh cement concrete OPC PC 42.5, the hardening time of cement slurry was significantly prolonged due to the synergistic retarding effect of sugar, colloid and total cellulose in the filter mud. In addition, the compressive strength of cement concrete mixed with the filter mud in the early stage (<10 days), middle stage (10–100 days) and later stage (180 days) was significantly higher than that of cement concrete and cement concrete mixed with commercial asphalt lignosulfonate. These results showed that the filter mud in molasses could realise harmless and resource utilisation, which could promote the comprehensive utilisation of molasses.