Silicate Shell Research Articles

Variations of Heat Flux and Elastic Thickness of Mercury From 3‐D Thermal Evolution Modeling

AbstractMercury's low obliquity and 3:2 spin‐orbit resonance create a surface temperature distribution with large latitudinal and longitudinal variations. These propagate via thermal conduction through the thin silicate shell influencing the interior temperature distribution. We use 3‐D thermal evolution models to investigate the effects of lateral variations of surface temperature and crustal thickness on the surface and core‐mantle boundary (CMB) heat fluxes, and elastic thickness distribution. Surface temperature variations cause a long‐wavelength perturbation of the heat fluxes, as well as of the elastic lithosphere thickness, while variations in crustal thickness affect these quantities at small spatial scales. Like the surface temperature, the present‐day CMB heat flux pattern is characterized primarily by spherical harmonics of degrees two and four, which could affect dynamo generation. Placing robust constraints on the thermal evolution based on the available estimates of the age and thickness of the elastic lithosphere remains challenging due to their large uncertainties.

Efficient extraction of refractory Cr from stainless steel dust by sodium persulfate oxidation roasting

Stainless steel dust (SSD) contains a high content of Cr and is listed as hazardous solid waste. However, SSD is mainly stockpiled in legacy waste sites due to its complexity and lack of investigation. Herein we comprehensively investigates the microscopic interaction between heavy metals and coexisting phases of SSD from the electric arc furnace (EAF). Furthermore, a new approach for extracting Cr from SSD was developed for the first time. It was found that SSD is enriched with Cr, Ni, Mn, and Zn. Most of these heavy metals are bound to stable spinel (e.g., FeCr2O4) and encapsulated by silicate. Using Na2S2O8 as the flux (1–24 mmol), under roasting at 350–750 °C in the air for 0.25–6 h, efficient heavy metal extraction can be achieved (Cr-80 %, Ni-86 %, Mn-93 %, Zn-94 %) at 650 °C for 1h. During the roasting processes, the silicate shell was broken, which facilitated the mass transfer of the oxidant. Fe(II) was oxidized to Fe(III) and collapsed the spinel structure, releasing the heavy metals during the following acid leaching. The total mass of SSD is reduced by 90–95 %, and detoxification of SSD is achieved after processing. In conclusion, efficient extraction refractory metals in SSD by Na2S2O8 roasting and the mechanism was elucidated for the first time. This method might also be applied for the treatment of other slags/ash waste that have a stable spinel structure and are encapsulated by silicate.

Mercury Ion Selective Adsorption from Aqueous Solution Using Amino-Functionalized Magnetic Fe2O3/SiO2 Nanocomposite.

This study focuses on the development of new amino-functionalized magnetic Fe2O3/SiO2 nanocomposites with varying silicate shell ratios (1:0.5, 1:1, and 1:2) for the efficient elimination of Hg2+ ions found in solutions. The Fe2O3/SiO2-NH2 adsorbents were characterized for their structural, surface, and magnetic properties using various techniques, including Fourier transform infrared spectrum (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Braunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), zeta-potential, and particle size measurement. We investigated the adsorption circumstances, such as pH, dosage of the adsorbent, and duration of adsorption. The pH value that yielded the best results was determined to be 5.0. The Fe2O3/SiO2-NH2 adsorbent with a silicate ratio of (1:2) exhibited the largest amount of adsorption capacity of 152.03 mg g-1. This can be attributed to its significantly large specific surface area of 100.1 m2 g-1, which surpasses that of other adsorbents. The adsorbent with amino functionalization demonstrated a strong affinity for Hg2+ ions due to the chemical interactions between the metal ions and the amino groups on the surface. The analysis of adsorption kinetics demonstrated that the adsorption outcomes adhere to the pseudo-second-order kinetic model. The study of adsorption isotherms revealed that the adsorption followed the Langmuir model, indicating that the adsorption of Hg2+ ions with the adsorbent occurred as a monomolecular layer adsorption process. Furthermore, the thermodynamic analyses revealed that the adsorption of Hg2+ ions using the adsorbent was characterized by a spontaneous and endothermic process. Additionally, the adsorbent has the ability to selectively extract mercury ions from a complex mixture of ions. The Fe2O3/SiO2-NH2 nanocomposite, which is loaded with metal, can be easily recovered from a water solution due to its magnetic properties. Moreover, it can be regenerated effortlessly through acid treatment. This study highlights the potential use of amino-functionalized Fe2O3/SiO2 magnetic nanoparticles as a highly efficient, reusable adsorbent for the removal of mercury ions from contaminated wastewater.

Performance and Microstructural Features of Sodium Silicate Shell Cured via Microfluidic Droplets of Citric Acid Solution

Performance and Microstructural Features of Sodium Silicate Shell Cured via Microfluidic Droplets of Citric Acid Solution

Preparation of hydrated calcium silicate phase change microcapsules and its application of temperature regulation in deep-water natural gas hydrate layer cementing process

The effective hydration of cement at low temperatures is a critical factor affecting the sealing stability of the cement sheath. Effective hydration of cement slurry is typically accompanied by significant exotherm, and can cause the decomposition of natural gas hydrates, ultimately leading to gas migration and affecting cementing quality. To ensure effective hydration with low exothermic cement slurry, hydrated calcium silicate (C-S-H) shell phase change microcapsules (TDCSH) were prepared by oil-in-water emulsification with chemical precipitation. Compared with traditional phase change microcapsule with polymer shell, the rough C-S-H shell with large surface area improves the thermal conductive area of the microcapsules and their compatibility with the cement composition. Results showed that the TDCSH has a high phase change enthalpy of 169.9 J/g and 65.25% encapsulate efficiency compared to other inorganic shell materials. Furthermore, the addition of 3% TDCSH can reduce the hydration temperature of cement by 3.9°C and increase the compressive strength by 19.0% under the curing condition of 20°C. The mechanism of action of microcapsules in cement was analyzed. The results showed that the incorporation of TDCSH reduced the heat of hydration of cement while promoting the generation of more hydration products and increased the compressive strength of cement.

Heterogenity of planetesimal collisional plume probed by glass inclusions in metal globules of Sierra Gorda 013, an unusual CBa‐like chondrite

AbstractMetal‐rich carbonaceous CB chondrites are generally assumed to be materials accreted from the gas–dust plume formed in catastrophic collisions of planetesimals, at least one of which was differentiated into a metal core and silicate shell. Micron‐sized inclusions of siliceous alkali‐rich glasses associated with sulfides were found in the metal globules of the Sierra Gorda 013 (SG 013), a CBa‐like chondrite. These inclusions are unusual carriers of volatile alkalis which are commonly depleted in CB chondrites. The inclusions are presented by two types: (1) Al‐bearing Nb‐poor glass associated with daubréelite and (2) Nb‐bearing Ca,Al,Mg‐poor glass associated with an unknown Na‐bearing Cr‐sulfide. The glass compositions do not correspond to equilibrium condensation, evaporation, or melting. The Nb‐bearing glass has a superchondritic Nb/Ta ratio (31) most likely indicating the fractionation of Nb and Ta in the high‐temperature gas–dust impact plume due to condensation from vapor or evaporation of precursor Nb‐rich particles. The glasses are interpreted as reaction products between refractory plume condensate particles (or possibly planetary or chondritic solids) with relatively low‐temperature K‐Na‐Si‐rich gas in oxidized conditions, possibly in a common plume vapor reservoir. Compositional differences indicate that the glasses and sulfides originated from several different sources under different fO2, fS2, andTconditions and were likely combined together and transported to the metal globule formation region by material flows in the heterogeneous impact plume. The glass–sulfide particles were enclosed in the globules aggregated from smaller solid or molten metal grains. The metal globules were further melted during transport to the high‐temperature plume region or by plume shockwave heating. Thus, the composition of the glasses, the host metal, and the main mass of SG 013 shows dynamic heterogeneity of physical conditions and impact plume composition after a large‐scale planetesimal collision.

Long-term internal erosion mechanism of organic matter in sediments solidified by cement, lime, and metakaolin

In applications of stabilized/solidified (S/S) sediments, the organic matter inside the original sediments will decompose and release fulvic acid (FA) and humic acid (HA) gradually, which may reduce the durability of the S/S sediments. It is critical to understand the long-term internal erosion mechanism to improve the durability of S/S sediments. Thus, S/S sediments solidified by commonly used cement, lime, and metakaolin were first prepared in the laboratory. Reasonable proportioning of the additives was determined through orthogonal tests. Unconfined compression strength tests, measurements of organic environment indexes and chemical environment indexes, and scanning electron microscopy analysis were then conducted after different curing periods of the S/S sediments to explore the erosion mechanism. The following results and conclusions were obtained. 1) The microstructure of S/S sediments is composed of a sediment aggregate core, a hydrated calcium silicate (CSH) shell covering the core, and calcium hydroxide (CH) submerged in the CSH shell. 2) HA and FA are released gradually by organic matter decomposition inside the core and are consumed by neutralization reactions with solidification products. 3) The dissipation process of organic matter and the induced damage process of S/S sediments can be partitioned into three stages: in the first stage, HA and FA jointly neutralize the solidification products inside the CSH shell, the CSH shell is eroded gradually, and the S/S sediments lose strength gradually; in the second stage, the neutralization reactions are still inside the CSH shell, but only occur between FA (not HA) and the solidification products, the CSH shell breaks down at the end of this stage, but the S/S sediments do not lose much strength until the end point; and in the third stage, neutralization reactions take place outside the CSH shell between HA (but not FA) and the solidification products, and the S/S sediments lose strength dramatically. It was also concluded that HA (rather than FA) is more likely to neutralize solidification products in a more alkaline environment; HA has much stronger chemical affinity with Ca2+ ions than FA; HA controls the strength loss of S/S sediments, whereas FA controls the working status of HA; and the developments of HA content and Ca2+ ion concentration reflect the strength loss of S/S sediments.

A Digital Light Microscopic Method for Diatom Surveys Using Embedded Acid-Cleaned Samples

Diatom identification and counting by light microscopy of permanently embedded acid-cleaned silicate shells (frustules) is a fundamental method in ecological and water quality investigations. Here we present a new variant of this method based on “digital virtual slides”, and compare it to the traditional, non-digitized light microscopy workflow on freshwater samples. We analysed three replicate slides taken from six benthic samples using two methods: (1) working directly on a light microscope (the “traditional” counting method), and (2) preparing “virtual digital slides” by high-resolution slide scanning and subsequently identifying and labelling individual valves or frustules using a web browser-based image annotation platform (the digital method). Both methods led to comparable results in terms of species richness, diatom indices and diatom community composition. Although counting by digital microscopy was slightly more time consuming, our experience points out that the digital workflow can not only improve the transparency and reusability of diatom counts but it can also increase taxonomic precision. The introduced digital workflow can also be applied for taxonomic inter-expert calibration through the web, and for producing training image sets for deep-learning-based diatom identification, making it a promising and versatile alternative or extension to traditional light microscopic diatom analyses in the future.

Highly effective remediation of high arsenic-bearing wastewater using aluminum-containing waste residue

Wastewater from non-ferrous metal smelting is known as one of the most dangerous sources of arsenic (As) due to its high acidity and high arsenic content. Herein, we propose a new environmental protection process for the efficient purification and removal of arsenic from wastewater by the formation of an AlAsO4@silicate core-shell structure based on the characteristics of aluminum-containing waste residue (AWR). At room temperature, the investigation with AWR almost achieved 100% As removal efficiency from wastewater, reducing the arsenic concentration from 5500 mg/L to 52 μg/L. With Al/As molar ratio of 3.5, the structural properties of AWR provided good adsorption sites for arsenic adsorption, leading to the formation of arsenate and insoluble aluminum arsenate with As. As-containing AWR silicate shells were produced under alkaline conditions, resulting in an arsenic leaching concentration of 1.32 mg/L in the TCLP test. AWR, as an efficient As removal and fixation agent, shows great potential in the treatment of copper smelting wastewater, and is expected to achieve large-scale industrial As removal.

Influence of Megaregolith on the Thermal Evolution of Mercury’s Silicate Shell

A so-called megaregolith layer that is considered to be produced by continuous impacts in Mercury’s early stages is integrated into the thermal evolution models of Mercury to study its influence on the thermal evolution of Mercury’s silicate shell. This research first implements a one-dimensional parametric global thermal evolution model. Our results indicate that megaregolith directly affects the thermal evolution of Mercury’s silicate shell by virtue of its good insulation performance. The way megaregolith exerts its influence is by prolonging the process of partial melting and reducing the heat loss, resulting in a thicker crust and thinner stagnant lid. As for the deep parts of the silicate shell, it is suggested that more energy is taken away from the mantle due to the longer partial melting, leading to lower temperatures below the crust compared with the case in the absence of megaregolith, which further helps to advance the formation time of the inner core and promote its final size. In addition, we also carry out a simplified two-dimensional mantle convection simulation as a supplement to the one-dimensional model. The two-dimensional simulation depicts a typical mantle plume fractional melting scenario. Our calculations indicate that megaregolith may be key to the long-term volcanic activities on Mercury. As far as the megaregolith itself is concerned, the thermal structure of this particular layer is more sensitive to thermal conductivity, suggesting that for such a highly fragmented structure, the thermal conductivity coefficient plays a key role in its evolution. Our work emphasizes the importance of megaregolith to the evolution of Mercury.

An inorganic origin of the “oil-source” rocks carbon substance

On the basis of an inorganic concept of the petroleum origin, the phase relationships of crystalline kerogens of black shales and liquid oil at the physicochemical conditions of a typical geobarotherm on the Texas Gulf Coast are considered. At the conditions of the carbon dioxide (CO2) high fluid pressure, the process of oil transformation into kerogens of varying degrees of “maturity” (retrograde metamorphism) takes place with decreasing temperature and hydrogen pressure. Kerogen generation in black shale rocks occurs by the sequential transition through metastable equilibria of liquid oil and crystalline kerogens (phase “freezing” of oil). The upward migration of hydrocarbons (HC) of oil fluids, clearly recorded in the processes of oil deposit replenishment in oil fields, shifts the oil ↔ kerogen equilibrium towards the formation of kerogen. In addition, with decreasing of the hydrogen chemical potential as a result of the process of high-temperature carboxylation and low-temperature hydration of oil hydrocarbons, the “mature” and “immature” kerogens are formed, respectively. The phase relationships of crystalline black shale kerogens and liquid oil under hypothetical conditions of high fluid pressure of the HC generated in the regime of geodynamic compression of silicate shells of the Earth in the result of the deep alkaline magmatism development. It is substantiated that a falling of hydrogen pressure in rising HC fluids will lead to the transformation of fluid hydrocarbons into liquid oil, and as the HC fluids rise to the surface, the HC ↔oil ↔ kerogen equilibrium will shift towards the formation of oil and kerogen. It is round that both in the geodynamic regime of compression and in the regime of expansion of the mantle and crust, carboxylation and hydration are the main geochemical pathways for the transformation of oil hydrocarbons into kerogen and, therefore, the most powerful geological mechanism for the black shale formations.

Did the cessation of convection in Mercury's mantle allow for a dynamo supporting increase in heat loss from its core?

Mercury's large core generates a magnetic field and harbors a solidified inner component. These features constrain models of the planet's thermal history. The mantle provides the boundary condition on Mercury's core that determines heat loss. Recent studies suggest Mercury's mantle may have a higher thermal diffusivity than the silicate shells of other rocky bodies due to iron depletion. Considering the role of diffusivity, we model Mercury's mantle starting from a post magma-ocean state by calculating core-mantle boundary heat flow and the ratio of inner-core boundary radius to core-mantle boundary radius, fc, for periods comparable to the age of the solar system. Core-mantle boundary (CMB) heat flow is calculated using 3D mantle convection simulations for thermal diffusivities, κ, ranging from 1.0 - 3.0 ×10−6 m2/s and initial radiogenic uniform mantle heating rates, χ, of 0 - 40 pW/kg (that decay with a 3 Gyr half-life). Several scenarios can unfold for the range of parameters considered: these include cases featuring both the cessation of mantle convection and its continuation at 4.5 Gyr. We map a trend in κ - χ space and find that for some parameters present-day core heat flux and inner-core size estimates are satisfied for a Mercurian mantle that is cooling by conduction. The influence of initial sulfur fraction in the core was examined for a subset of cases. For a sulfur fraction of 0.10, fc falls between 0.1 and 0.55 which corresponds to planetary radius contractions below 7 km (since the Late Heavy Bombardment). However, fc exceeds 0.55 for a lower initial sulfur fraction and results in planetary contraction in excess of 7 km. In general, we find that the mean core heat flux reaches a temporal local minimum when the mantle transitions from a convective to a conductive regime and subsequently climbs before decreasing. The transition to conduction is delayed with increased mantle internal heating rate but the maximum mean heat flux from the core into the conducting and cooling mantle is always greater than the heat flux observed at the cessation of the stagnant-lid convection. We find that for an initially more vigorously convecting mantle the onset of inner-core growth is earlier while the basal heat flux is marginally reduced at present day. In general, we find that current-day conductive cooling of the Mercurian mantle can satisfy estimates on Mercury's core heat loss inferred from the strength of its magnetic field while also satisfying the limits on the present-day size of its inner core.

Installation of Bored Piles with a Protective Silicate Shell of a New Design in Saline Silty-Clayey Soils

Designing advanced methods of corrosion protection and increasing the bearing capacity of pile foundations on saline clayey soils is a priority geotechnical task in Kazakhstan. The formation of a suffusion-resistant waterproof shell was achieved by silicatization of a borehole before concreting, by the installation of a mold into the borehole and the impregnation of a sodium silicate solution into the space between the mold and the soil under pressure. After coagulation of the silicate solution, the mold was removed and the formed shell was filled with corrosion-resistant concrete. Full-scale static pile load tests were conducted in the construction site “Retaining wall on Mount Koktobe” in Almaty. The bearing capacity of the piles with the protective silicate shell exceeded the bearing capacity of an ordinary pile by 2.5 times on average without wetting the site, and 3.2 times after prolonged wetting. The numerical model had a close relationship with the average experimental curve obtained when conducting six static pile load tests with the protective shell. A large economic effect of the developed piling technology with a protective shell was achieved, with a significant reduction in the cost of piling, equal to 27.85%.

CO2 capture behavior and chemical structure of the alkali zirconate-silicate hybrid sorbent from ZrSiO4 by alkali activation method

The zirconate-silicate hybrid as CO2 capture sorbent at high temperature were decomposed from ZrSiO4 by NaOH and KOH. The chemical structure and CO2 adsorption/desorption dynamics of zirconate-silicate hybrid were studied by the Fourier transform infrared, X-ray photoelectron spectroscopy and the thermogravimetric measurements. The results show that alkali divides ZrSiO4 into ZrO2 and Si-OH groups, then Si-OH groups diffuse into molten alkali and condensate to form a silicate shell with CO2 capture capacity on the surface of alkali activation products. The electron-donating ability of the molten alkali determines the chemical structure and the CO2 storage capacity of sorbents. When the ratio of NaOH to ZrSiO4 is 6:1, the sorbent with the optimal chemical structure for CO2 capture can be acquired after the alkali activation reaction. The CO2 capture process is kinetically controlled by metal cation diffusion after the carbonate-oxide external shell is formed, and the diffusion process is more dependent on the chemical structure of silicates in the zirconate-silicate hybrid than CO2 direct chemisorption reaction.

Highly effective remediation of high-arsenic wastewater using red mud through formation of AlAsO4@silicate precipitate

High-arsenic wastewater derived from the metallurgical industry of nonferrous minerals is one of the most dangerous arsenic (As) sources that usually follow the emission of massive hazardous arsenic-bearing wastes. Considering the properties of red mud (RM), we propose an alternative and environmentally friendly method for the efficient remediation of high-arsenic wastewater using RM through formation of AlAsO4@silicate precipitate, aiming at ''zero-emission of hazardous solid waste''. The results show nearly 100% of arsenic could be stepwisely removed from high-arsenic wastewater and reduce the arsenic concentration from 6100 mg/L to 40 μg/L using RM at room temperature. The highest arsenic removal capacity of RM reaches 101.5 mg/g at a RM-to-wastewater ratio of 40 g/L due to the superior arsenic adsorption and the co-precipitation of arsenate and Al3+ to form insoluble aluminum arsenate. The silicate shell of arsenic-loaded RM created at an alkaline condition acts as an arsenic stabilizer, resulting in a leached arsenic concentration of 1.2 mg/L in TCLP tests. RM acts as a highly effective arsenic remover and stabilizer for the disposal of high-arsenic wastewater. It shows great potential for the remediation of wastewater containing heavy metals with varying concentrations to produce clean water available for industrial purpose.

Effect of pore adjustable hydrophilic nickel coated polyethylene membrane on the performance of aqueous naphthoquinone based redox flow batteries

The surface of porous polyethylene (SB-PE) membrane is modified with nickel coating using a hydrothermal method (SB-PE-Ni-x membrane). To optimize effects of pore size and hydrophilicity on properties of SB-PE-Ni-x, the amount of included nickel is varied. According to evaluations, structure of SB-PE-Ni-x is well preserved even under strong alkaline due to the formation of nickel silicate shell. The nickel silicate shell induces the preservation of stability and hydrophilicity and increase in ionic conductivity, while porosity and pore size of SB-PE-Ni-x are reduced from 67.4% and 0.819 µm (SB-PE) to 57.9% and 0.557 µm (SB-PE-Ni-100). Chemical characterizations show that when nickel is coated onto SB-PE, porous structure and chemical bonding of SB-PE-Ni-x remain unchanged with high water uptake (32.5%) even after alkali treatment. This is evidence of high ionic conductivity. The performances of aqueous organic redox flow batteries (AORFBs) using mixed naphthoquinone and potassium ferrocyanide dissolved in potassium hydroxide are then investigated with SB-PE and SB-PE-Ni-x membranes. As a result, AORFB using SB-PE-Ni-50 shows high energy efficiency (80%) and low capacity loss rate (0.0235 Ah∙L−1 per cycle). This is because SB-PE-Ni-50 has optimal pore size showing less cross-over of active materials and high ionic conductivity.

Intrinsic Effect of Nanoparticles on the Mechanical Rupture of Doubled-Shell Colloidal Capsule via In Situ TEM Mechanical Testing and STEM Interfacial Analysis.

The discovery of Pickering emulsion templated assembly enables the design of a hybrid colloidal capsule with engineered properties. However, the underlying mechanisms by which nanoparticles affect the mechanical properties of the shell are poorly understood. Herein, in situ mechanical compression on the transmission electron microscope and aberration-corrected scanning transmission microscope are unprecedentedly implemented to study the intrinsic effect of nanoparticles on the mechanical properties of the calcium carbonate (CaCO3 )-decorated silica (SiO2 ) colloidal capsule. The stiff and brittle nature of the colloidal capsule is due to the interfacial chemical bonding between the CaCO3 nanoparticles and SiO2 inner shell. Such bonding strengthens the mechanical strength of the SiO2 shell (166 ± 14 nm) from the colloidal capsule compared to the thicker single SiO2 shell (310 ± 70 nm) from the silica hollow sphere. At elevated temperature, this interfacial bonding accelerates the formation of the single calcium silicate shell, causing shell morphology transformation and yielding significantly enhanced mechanical strength by 30.9% and ductility by 94.7%. The superior thermal durability of the heat-treated colloidal capsule holds great potential for the fabrication of the functional additives that can be applied in the wide range of applications at elevated temperatures.

The Milton pallasite and South Byron Trio irons: Evidence for oxidation and core crystallization

The link between the Milton pallasite and the South Byron Trio irons is examined through metallography and metallogaphic cooling rates; major, minor, and trace element compositions of metal; inclusion mineralogy and mineral compositions; and oxygen isotopic compositions. The metallic hosts of these Ni-rich meteorites (18.2–20.3 wt% Ni) are dominated by plessite with spindles of kamacite and schreibersite. The presence of ∼50 nm wide tetrataenite and absence of high-Ni particles in the cloudy zone in Milton suggest cooling of ∼2000 K/Myr or >10,000 K/Myr. Compositionally, the metallic host in all four meteorites exhibits modest (1–2 orders of magnitude compared to CI chondrites) depletions of volatile elements relative to refractory elements, and marked depletions in the redox sensitive elements W, Mo, Fe, and P. Oxygen isotopic compositions (Δ 17 O) are, within uncertainty, the same for the Milton and the South Byron Trio and for IVB irons. Similarities in metallography, metal composition, inclusion mineralogy, and oxygen (Δ 17 O), molybdenum and ruthenium isotopic composition suggest that the Milton pallasite and South Byron Trio irons could have originated on a common parent body as chemically distinct melt, or on separate parent bodies that experience similar cosmochemical and geochemical processes. The Milton pallasite and South Byron Trio irons share a number of properties with IVB irons, including metallography, enrichment in highly siderophile elements and nickel, inclusion mineralogy and oxygen isotopic composition, suggesting they formed in a similar nebular region through common processes, although Milton and the South Byron Trio did not experience the dramatic volatile loss of the IVB irons. Depletions in W, Mo, Fe, and P relative to elements of similar volatility likely result from oxidation, either in the nebula prior to accretion or on the parent body during melting. Oxidation of ∼73 wt% Fe is indicated, with a correspondingly FeO-rich mantle and smaller core. If Milton and the South Byron Trio sample a common core, Milton formed near the surface of the core after stripping of the silicate shell and may have experienced rapid solidification and contamination by an impactor. The molten core, from which the South Byron Trio irons crystallized, solidified from the outside in.

Angiogenesis-promoted bone repair with silicate-shelled hydrogel fiber scaffolds.

Promoting angiogenesis is a key strategy for stimulating the repair of damaged tissues, including bone. Among other proangiogenic factors, ions have recently been considered a potent element that can be incorporated into biomaterials and then released at therapeutic doses. Silicate-based biomaterials have been reported to induce neovascularization through vascular endothelial growth factor signaling pathway, potentiating acceleration of bone regeneration. Here, we designed a silicate-shelled hydrogel fiber scaffold with a hard/soft layered structure to investigate the possibility of silicate coating on biopolymer for enhancing biological properties. An alginate hydrogel was injected to form a fiber scaffold with shape-tunability that was then coated with a thin silicate layer with various sol-gel compositions. The silicate/alginate scaffold could release calcium and silicate ions, and in particular, silicate ion release was highly sustainable for over one week at therapeutically relevant levels. The ionic release was highly effective in stimulating the mRNA expression of angiogenic markers (VEGF, KDR, eNOS, bFGF, and HIF1-α) in endothelial cells (HUVECs). Moreover, the in vitro tubular networking of cells was significantly enhanced (1.5 times). In vivo implantation in subcutaneous tissue revealed more pronounced blood vessel formation around the silicate-shelled scaffolds than around silicate-free scaffolds. The presence of a silicate shell was also shown to accelerate acellular mineral (hydroxyapatite) formation. The cellular osteogenesis potential of the silicate/alginate scaffold was further proven by the enhanced expression of osteogenic genes (Col1a1, ALP and OCN). When implanted in a rat calvarium defect, the silicate-shelled scaffold demonstrated significantly improved bone formation (2-3 times higher in bone volume and density) with a concurrent sign of proangiogenesis. This work highlights that the surface-layering of silicate composition is an effective approach for improving the bone regeneration capacity of polymeric hydrogel scaffolds by stimulating ion-induced angiogenesis and providing bone bioactivity to the surface.

(Invited) Nanoscale Chemistry and Electrochemistry with Porous Silicon Nanoparticles

Prepared by electrochemical or chemical etch of crystalline silicon, porous silicon is an intrinsically strong reducing agent, enabling electroless deposition of noble metals via galvanic displacement. In addition to acting as an electron source, the oxidation of silicon generates water-soluble silicic acid as a chemical byproduct. This combination of electrochemistry and chemistry can be harnessed to form new, functional structures that with interesting applications in sensors, nanomedicine, and catalysis. A biological analog for these chemical and electrochemical processes can be found in cellular autophagy, where cellular components such as proteins and organelles are turned over to generate new cellular functions. The reducing ability of elemental silicon and the low solubility of silicate byproducts allow for inorganic autophagy in silicon nanostructures. For example, in the presence of silver or palladium ions, metal nanoparticles are formed by electroless deposition within a porous Si nanoparticle, generating composite nanoparticles with dimensions and properties controlled by the porous nanostructure. One approach to control the size of the resulting metallic nanoparticles is to use ammine complexes of the metal salt precursors. When the metal coordination complex is reduced, it releases free ammonia that locally dissolves the SiO2 reaction byproduct that would otherwise lead to heterogeneous metal deposition. The resulting materials can be used as catalysts, imaging probes or as in vivo antibacterial agents. Alternatively, dissolution of Si generates orthosilicic acid, which precipitates in the presence of calcium or magnesium ion to form a structural silicate shell that can be used to trap molecules or other nanostructures for therapeutic or analytic applications. This presentation will discuss the chemistry, the electrochemistry, and the photochemistry of nanostructured porous silicon, with emphasis on the self-destruction and reconstruction processes that can be harnessed for the above-mentioned applications.