High Si Research Articles

The role of Si in enhancing the stability of residual austenite and mechanical properties of a medium carbon bainitic steel

In this work, two bainitic steels with medium carbon content were developed by adding different Si. The mechanical properties of the two test steels and the stability of their retained austenite were studied, and the influence of Si in the steels was discussed. The results show that the film-like retained austenite of the high Si bainitic steel is greatly increased compared with that of the low Si bainitic steel and that the C content is increased, effectively preventing crack propagation and significantly improving the comprehensive mechanical properties. Due to the different Si content in the test steels, the orientation relationship of austenite in the steels has changed, and when the Si content is increased from 0.7 wt% to 1.4 wt%, the variant selection of bainite becomes weaker. Moreover, the increase of Si content not only inhibits the precipitation of carbides but also promotes the accumulation of C in the austenite, which improves the stability of the retained austenite.

Fatigue Properties at Elevated Temperatures of Secondary Tempered Nanostructured Bainite: A Study of Deformation Mechanisms

Nanostructured bainitic steel obtained through austempering or bainitic transformation of high Si steels consists of bainitic ferrite and carbon‐enriched retained austenite. Secondary tempering of those microstructures tailors their mechanical properties through its unique nanostructure and austenite stability. Herein, fatigue and tensile properties of a nanobainitic steel in different secondary tempering conditions are presented and the results are discussed based on the deformation mechanisms taking place due to the microstructure evolution during secondary tempering. Influence of secondary tempering and elevated testing temperature on tensile and fatigue properties at room temperature and 250 °C is presented. Based on the present deformation, mechanism results are discussed supported by microstructure evolution results obtained through dilatometry, X‐ray diffraction, and microscopy. Depending on secondary tempering temperature, main influencing mechanisms are martensite formation after secondary tempering during cooling, transformation‐induced plasticity effect, and precipitation hardening obtained by secondary tempering.

A comparison of spreader penetration depth and load required in curved canal using two types of spreaders

The aim of the present study was to compare nickel titanium and stainlesssteel spreaders penetration depth and load in lateral compaction. Thirty curved mesialcanals of extracted mandibular molars were used in the study. The canals wereprepared using step-back technique with Gates-Glidden. Afterward the teeth weredivided randomly into 2 groups. In part 1 of the study, the force required to inserteach spreader to within 1 mm of the working length in an empty canal was measured .In part 2, the force required to insert each spreader to within 2 mm of the workinglength was measured in canal containing a master cone. ln part 3, the depth ofpenetration of each spreader with a master cone in place using a 1.5 kg force wasmeasured. Using a t-test for paired samples, the results from pan 1 showed that nickeltitanium spreader required high significantly less force than stainless steels reader P<0.01 . ln part 2, a nickel titanium s reader re uired high si niticantl lessforce than a stainless steel spreader .As expected in part 3, a nickel titanium spreaderpenetrated to a significantly high depth than stainless steel spreader (P<0.0l

High capacity and high rate capability Si anodes encapsulated with camphor-derived graphene for Li ion batteries

Future Li ion battery technologies demand novel design strategies for Li ion battery anode overlays with shorter ion diffusion channels, better interfacial resistance and enlarged electrode–electrolyte interface. This is especially significant when it comes to alloy anodes like Si, Ge etc where the ultra-high theoretical capacities are unable to be utilized owing to their huge volume expansion during the process and lower conductivity. A new strategy is introduced to synthesize Si nanoparticle based composite with graphene and carbon. Encapsulation of a homogeneous graphene layer imparts the anodes with high reversible capacity, outstanding stability and very high rate capability. The optimal samples exhibit an excellent capacity as high as 3327 mAhg-1and superior rate capability. The cyclic stability of the system was also outstanding with a capacity retention of 84% at the end of 100 cycles while neglecting the initial stabilizing period the capacity retention reaches upto 97%.

Nutrient enrichment alters phytoplankton biomass and composition via silicon limitation

Despite management efforts, anthropogenic nutrient enrichments continue to enhance phytoplankton blooms worldwide. Release of nitrogen and phosphorus compounds not only provides surplus of nutrients but also disbalances their stoichiometry. Declines in the relative availability of dissolved silicon might induce limitation in diatoms, major primary producers with silicified shells. We studied experimentally how nutrient enrichment and resulting decline in dissolved silicon to nitrogen ratios (Si:N) affect the structure and functioning of natural plankton communities. Nitrate was added to create a range of Si:N ratios and phosphate was supplied in Redfield ratio to nitrogen. We also manipulated copepod abundance to understand the top-down effects on communities experiencing nutrient enrichment. Nitrogen and phosphorus additions resulted in a steep phytoplankton biomass increase, followed by a post-bloom decline. Phytoplankton bloom biomass was higher in high nitrogen treatments but during the post-bloom period this trend switched. Biomass was sustained longer in high Si:N treatments, indicating that silicon limitation terminates the bloom. Many diatom species did not benefit from nitrogen and phosphorus enrichment and diatom dominance ceased below Si:N of 0.4:1. Under high grazing pressure, silicate was taken up faster suggesting that silicification is important in diatom defense. Copepods shaped plankton communities via feeding on dinoflagellates, chlorophytes and the diatom Skeletonema costatum but there was no significant effect of nitrogen and phosphorus enrichment on copepod abundance. Our results, combined with previous studies, show that while nutrient concentrations define the total phytoplankton bloom biomass, resource ratios are important in sustaining biomass and determining community structure and composition.

Trace Silicon Determination in Biological Samples by Inductively Coupled Plasma Mass Spectrometry (ICP-MS): Insight into the Volatility of Silicon Species in Hydrofluoric Acid Digests for Optimal Sample Preparation and Introduction to ICP-MS

A method for the determination of trace levels of silicon from biological materials by inductively coupled plasma mass spectrometry (ICP-MS) has been developed. The volatility of water-soluble silicon species, hexafluorosilicic acid (H2SiF6), and sodium metasilicate (Na2SiO3) was investigated by evaporating respective solutions (50 µg/mL silicon) in HNO3), nitric acid + hydrochloric acid (HNO3 + HCl), and nitric acid + hydrochloric acid + hydrofluoric acid (HNO3 + HCl + HF) at 120 °C on a hot-block to near dryness. The loss of silicon from H2SiF6 solutions was substantial (>99%) regardless of the digestion medium. Losses were also substantial (>98%) for metasilicate solutions heated in HNO3 + HCl + HF, while no significant loss occurred in HNO3 or HNO3 + HCl. These results show that H2SiF6 species were highly volatile and potential losses could confound accuracy at trace level determinations by ICP-MS if digestates prepared in HF are heated to eliminate HF. Among the various matrices comprising major elements, sodium appeared to be effective in reducing silicon loss from H2SiF6 solutions. Excess sodium chloride (NaCl) matrix provided better stability, improving silicon recoveries by up to about 80% in evaporated HF digestates of soil and mine waste samples, but losses could not be fully prevented. To safely remove excess acids and circumvent the adverse effects of excess HF (e.g., risk of high Si background signals), a two-step digestion scheme was adopted for the preparation of biological samples containing trace silicon levels. A closed-vessel digestion was performed either in 4 mL of concentrated HNO3 and 1 mL of concentrated HCl or 4 mL of concentrated HNO3, 1 mL of concentrated HCl and 1 mL of concentrated HClO4 on a hot plate at 140 °C. Digestates were then evaporated to incipient dryness at 120 °C to remove the acids. A second closed-vessel digestion was carried out to dissolve silicates in 0.5 mL of concentrated HNO3 and 0.5 mL of concentrated HF at 130 °C. After digestion, digestates were diluted to 10 mL. The solution containing about 5% HNO3 and 5% HF was directly analyzed by ICP-MS equipped with an HF-inert sample introduction system. The limit of detection was about 110 µg/L for 28Si when using the Kinetic Energy Discrimination (KED) mode. The method was used to determine silicon in various plant and tissue certified reference materials. Data were acquired for 28Si using KED and standard (STD) modes, and 74Ge and 103Rh as internal standard elements. There was not any significant difference between the accuracy and precision of the results obtained with 74Ge and 103Rh within the same measurement mode. Precision, calculated as relative standard deviation for four replicate analyses, varied from 5.3 (tomato leaves) to 21% (peach leaves) for plant and from 2.2 (oyster tissue) to 33% (bovine liver) for tissue SRM/CRMs. Poor precision was attributed to material heterogeneity and the large particle size distribution. An analysis of lung tissue samples from those with occupational exposure to silica dust revealed that tissues possessed substantial levels of water-soluble silicates, but the most silicon was present in the particulate matter fraction.

Achieving superior grain refinement efficiency for Al–Si casting alloys through a novel Al–La–B grain refiner

Conventional Al–Ti–B and Al–Ti–C refiners fail to refine Al–Si casting alloys with high Si content due to the well-known “Si-poisoning” effect. Developing a novel grain refiner with superior grain refinement efficiency for Al–Si casting alloys is the research focus in recent years. In this work, a superior anti Si-poisoning α-Al grain refiner Al–2La–1B alloy with fine LaB6 particles was successfully fabricated via the aluminum melt reaction method. The microstructural evolution, grain refinement performance and refinement mechanisms of the Al–2La–1B alloy were comprehensively investigated based on the experiment results and first-principles calculations. The currently designed Al–2La–1B refiner presents supreme grain refinement efficiency on Al–Si casting alloys. The average grain size of Al–7Si alloy inoculated with 0.5% Al–2La–1B alloy can be refined to 67 ± 5 μm. The superior grain refinement performance can be attributed to the presence of fine LaB6 particles in the refiner. These particles are highly stable in Al–Si alloy melt and can directly act as the potent nucleation sites for α-Al due to the small lattice misfit and low interfacial energy. Moreover, the nucleation potency of the LaB6 particles will not be influenced by the solute Si element. Our work provides an effective strategy for designing a superior α-Al grain refiner for Al–Si casting alloys.

Geochemistry, Sr-Nd Isotope Compositions, and U-Pb Chronology of Apatite from Kimberlite in Wafangdian, North China Craton: Constraints on the Late Magmatic Processes

Diamondiferous kimberlites occur in the Wafangdian area in the eastern part of the North China Craton (NCC). In order to better constrain their magmatic source and emplacement time, we have investigated apatite from two kimberlites, i.e., the #110 dike kimberlite and the #50 root-zone kimberlite by measuring in situ their U–Pb and Sr–Nd isotopic compositions. The crystallization ages of the #110 and #50 apatites are 460.9 ± 16.8 Ma and 455.4 ± 19.3 Ma, respectively. For the #50 apatite, 87Sr/86Sr = 0.70453–0.70613 and εNd(t) = −2.74 to −4.52. For the #110 apatite, 87Sr/86Sr = 0.70394–0.70478 and εNd(t) = −3.46 to −5.65. Based on the similar distribution patterns of the rare earth elements (REEs) and the similar Sr-Nd isotope compositions of the apatite, it is believed that the #110 and #50 kimberlites have the same source region and the kimberlite magmas in Wafangdian were derived from an enriched mantle source (EMI). The primary magmatic composition has little effect on the emplacement pattern. It is more likely that the geological environment played an important role in controlling the retention and removal of volatile components (H2O and CO2). This led to the different evolutionary paths of the kimberlite magma in the later period, resulting in differences in the major element compositions of the apatite. High Sr concentrations may be associated with hydrothermal (H2O-rich fluid) overprinting events in the later magmatic period; the higher light rare earth element (LREE) concentration of the #50 apatite reflects the involvement of the REE3+ + SiO44− ⇔ Ca2+ + PO43− replacement mechanism. Two emplacement patterns of the #110 dike kimberlite (#110 apatite, low Sr, and high Si) and the #50 root-zone (#50 apatite, high Sr, and low Si) kimberlites were identified via major element analysis of the #110 apatite and #50 apatite.

High Peritumoral and Intratumoral T2 Signal Intensity in HER2-Positive Breast Cancers on Preneoadjuvant Breast MRI: Assessment of Associations With Histopathologic Characteristics.

BACKGROUND. Intratumoral necrosis and peritumoral edema are features of aggressive breast cancer that may present as high T2 signal intensity (T2 SI). Implications of high T2 SI in HER2-positive cancers are unclear. OBJECTIVE. The purpose of this study was to assess associations with histopathologic characteristics of high peritumoral T2 SI and intratumoral T2 SI of HER2-positive breast cancer on MRI performed before initiation of neoadjuvant therapy. METHODS. This retrospective study included 210 patients (age, 24-82 years) with 211 HER2 breast cancers who, from January 1, 2015, to July 30, 2022, underwent breast MRI before receiving neoadjuvant therapy. Two radiologists independently assessed cancers for high peritumoral T2 SI and high intratumoral T2 SI on fat-suppressed T2-weighted imaging and classified patterns of high peritumoral T2 SI (adjacent to tumor vs prepectoral extension). A third radiologist resolved discrepancies. Multivariable logistic regression analyses were performed to identify associations of high peritumoral and intratumoral T2 SI with histopathologic characteristics (associated ductal carcinoma in situ, hormone receptor status, histologic grade, lymphovascular invasion, and axillary lymph node metastasis). RESULTS. Of 211 HER2-positive cancers, 81 (38.4%) had high peritumoral T2 SI, and 95 (45.0%) had high intratumoral T2 SI. A histologic grade of 3 was independently associated with high peritumoral T2 SI (OR = 1.90; p = .04). Otherwise, none of the five assessed histopathologic characteristics were independently associated with high intratumoral T2 SI or high peritumoral T2 SI (p > .05). Cancers with high T2 SI adjacent to the tumor (n = 29) and cancers with high T2 SI with prepectoral extension (n = 52) showed no significant difference in frequency for any of the histopathologic characteristics (p > .05). Sensitivities and specificities for predicting the histopathologic characteristics ranged from 35.6% to 43.7% and from 59.7% to 70.7%, respectively, for high peritumoral T2 SI, and from 37.3% to 49.6% and from 49.3% to 62.7%, respectively, for high intratumoral T2 SI. Interreader agreement was almost perfect for high peritumoral T2 SI (Gwet agreement coefficient [AC] = 0.93), high intratumoral T2 SI (Gwet AC = 0.89), and a pattern of high peritumoral T2 SI (Gwet AC = 0.95). CONCLUSION. The only independent association between histopathologic characteristics and high T2 SI of HER2-positive breast cancer was observed between a histologic grade of 3 and high peritumoral T2 SI. CLINICAL IMPACT. In contrast with previously reported findings in broader breast cancer subtypes, peritumoral and intratumoral T2 SI had overall limited utility as prognostic markers of HER2-positive breast cancer.

Influence of swirl intensity on combustion dynamics and emissions in an ammonia-enriched methane/air combustor

Ammonia (NH3) has been widely considered as a promising carbon-free energy and hydrogen carrier for various applications. The large-scale direct utilization of NH3 as fuel in gas turbine engines is currently attracting significant interest, with strong focuses on improving the efficiency and stability of the system and reducing the emissions of pollutants. The present study experimentally examined the impacts of swirl intensity on combustion stability and emissions in an NH3-enriched premixed swirl-stabilized CH4/air combustor under a wide range of equivalence ratios. Simultaneous high-speed OH* chemiluminescence and particle image velocimetry measurements suggested that increasing swirl intensity resulted in more compact flame shapes and expanded the recirculation zone, which promoted flame stability at higher NH3 ratios. However, under specified conditions, enhancing swirl intensity could increase the instability frequency and amplitude of pressure oscillations. The flame dynamics exhibited different behaviors depending on the swirl intensity. At high swirl intensity, the flames underwent high-frequency, small-amplitude periodic motion. At low swirl intensity, the flames oscillated axially with large amplitude and low frequency. For flow dynamics, the stability of the vortex at high swirl intensity contrasted with the periodic vortex shedding at low swirl intensity. Furthermore, the two-dimensional Rayleigh index indicated that the dominant positive thermoacoustic coupling regions were located near the flame shear layers and flame tail at low and high swirl intensities, respectively. Finally, the experimental results showed that swirl intensity affected pollutant emissions by influencing the temperature of combustion chamber and gas mixing efficiency. The pathway of fuel-type NOx was found to be dominant in the NOx emission of the NH3/CH4/air flames.

Tetrahedral aluminum in tourmaline from a spinel-pargasite-metamorphosed mafic-ultramafic rock

Abstract Tourmaline is a widespread borosilicate mineral, which is well known for its variable chemistry. Although major amounts of octahedral Al in tourmaline is commonplace, the occurrence of significant amounts of tetrahedral Al is relatively rare. This paper focuses on tourmaline from the collection of the A.E. Fersman Mineralogical Museum (Russia) originated from Italy with up to 25% of Si replaced by Al at the tetrahedral site. The tourmaline is characterized by optical and scanning electron microscopy, Raman spectroscopy, infrared spectroscopy, Mössbauer spectroscopy, energy-dispersive and wavelength-dispersive X-ray analysis, laser ablation inductively coupled plasma optical emission spectrometry and single crystal X-ray diffraction. The studied tourmaline occurs as transparent dark blue crystals (with equant external morphology) up to 3 mm in size and forms veinlets cutting a (Mg,Al)-rich metamorphosed mafic-ultramafic rock (Mg≫Fe) composed of spinel, pargasite, clinochlore, phlogopite, and hydroxylapatite. The studied tourmaline meets the criteria defining magnesio-lucchesiite and can be compositionally formed via Tschermak-like ([6]Me2++[4]Si4+↔[6]Al3++[4]Al3+, where [6]Me2+=Mg, Fe) or plagioclase-like ([9]Ca2+ + [4]Al3+ ↔ [9]Na+ + [4]Si4+) substitutions. Zones with a relatively high Si content (Si-rich) have pronounced indications of dissolution, while silicon-depleted zones (Si-poor) overgrow Si-rich zones and eventually creates a visible replacement zone of the crystal. We suggest that Si-poor tourmaline result from the Si-rich tourmaline losing Si during a metasomatic process. The resulting empirical crystal-chemical formula for the Si-poor zone is: X(Ca0.95Na0.03□0.02)Σ1.00 Y(Mg1.08Al0.98Fe2+0.50Fe3+0.43)Σ3.00 Z(Al5.91Fe3+0.09)Σ6.00 T[(Si4.57Al1.43)Σ6.00O18] (BO3)3 V(OH)3 W[O0.95(OH)0.05]Σ1.00 (a = 15.9811(2), c = 7.12520(10) Å, R1 = 1.7 %) and for the Si-rich zone is: X(Ca0.89Na0.11)Σ1.00 Y(Mg1.55Al0.80Fe2+0.34Fe3+0.31)Σ3.00 Z(Al5.51Mg0.44Fe3+0.05)Σ6.00 T[(Si5.35Al0.65)Σ6.00O18] (BO3)3V(OH)3W[O0.93(OH)0.07]Σ1.00 (a=15.9621(3), c=7.14110(10) Å, R1=1.7 %). According to PT calculations of mineral assemblage stability and comparable data on synthetic [4]Al-rich tourmalines, the studied tourmaline was formed at 600–750 °C and 0.10-0.20 GPa. The formation of tetrahedral Al-rich tourmalines requires several unusual factors: (1) desilication of primary rocks and (2) high temperatures and relatively low pressures.

Magnesium silicate chimneys at the Strytan hydrothermal field, Iceland, as analogues for prebiotic chemistry at alkaline submarine hydrothermal vents on the early Earth

The Strytan Hydrothermal Field (SHF) in basaltic terrain in Iceland is one of the extant alkaline submarine hydrothermal vent systems favoured as analogues for where life on Earth may have begun. To test this hypothesis we analyse the composition, structure, and mineralogy of samples from hydrothermal chimneys generated at the SHF. We find that the chimney precipitates are composed of Mg-silicates including clays of the saponite-stevensite group (high Mg and Si, low Fe and Al), Ca-carbonates and Ca-sulfates. The chimneys comprise permeable structures with pores sizes down to 1 µm or less. Their complex interiors as observed with SEM (Scanning Electron Microscopy) and X-ray CT (computed tomography scanning), exhibit high internal surface areas. EDX (energy-dispersive X-ray spectroscopy) analysis reveals an increase in the Mg/Si ratio toward the chimney exteriors. Chemical garden analogue experiments produce similar Mg–silicate chimneys with porous internal structures, indicating that injection-precipitation experiments can be high-fidelity analogues for natural hydrothermal chimneys at the SHF. We conclude that SHF chimneys could have facilitated prebiotic reactions comparable to those proposed for clays and silica gels at putative Hadean to Eoarchean alkaline vents. Analysis of the fluid dynamics shows that these chimneys are intermediate in growth rate compared to faster black smokers though slower than those at Lost City. The SHF is proposed as a prebiotic alkaline vent analogue for basaltic terrains on the early Earth.

Experimental Hydrothermal Alteration of Rhyolite and Andesite at 325 °C and 300 Bar: Implications for a Potential Role of Volcanic Glass in the Fluid Composition in the Okinawa Trough

The experimental study of water–rock reactions under high-temperature and -pressure conditions is a useful approach to constrain controlling factors of the fluid composition in a natural hydrothermal system. Previous studies have focused mainly on the mid-ocean ridge fields, and the hydrothermal alteration of intermediate-to-felsic rocks has been less emphasized despite its potential importance in the fluid chemistry in an arc/back-arc basin setting. We examined the alteration processes of fresh rhyolite and andesite rocks collected from the middle and southern Okinawa Trough, respectively, at 325 °C and 300 bar (the estimated condition at the reaction zone in the fields), especially focusing on the behavior of silica between the solid and liquid phases. The experimental fluids are characterized by the high Si concentration up to 30 mM, indicating the substantial dissolution of volcanic glass in the analyzed rocks. The high Si concentration in the fluids was presumably buffered by amorphous silica, precipitated from the fluids as a precursor of hydrothermal quartz, during the experiments. Our results emphasize a previously overlooked role of volcanic glass/amorphous silica in the fluid composition in the Okinawa Trough and are consistent with the previous model of pumice replacement mineralization for the SMS deposit formation in the trough.

High mechanical strength Si anode synthesis with interlayer bonded expanded graphite structure for lithium-ion batteries

Despite advancements in silicon-based anodes for high-capacity lithium-ion batteries, their widespread commercial adoption is still hindered by significant volume expansion during cycling, especially at high active mass loadings crucial for practical use. The root of these challenges lies in the mechanical instability of the material, which subsequently leads to the structural failure of the electrode. Here, we present a novel synthesis of a composite combining expanded graphite and silicon nanoparticles. This composite features a unique interlayer-bonded graphite structure, achieved through the application of a modified spark plasma sintering method. Notably, this innovative structure not only facilitates efficient ion and electron transport but also provides exceptional mechanical strength (Vickers hardness: up to 658 MPa, Young’s modulus: 11.6 GPa). This strength effectively accommodates silicon expansion, resulting in an impressive areal capacity of 2.9 mA h cm−2 (736 mA h g−1) and a steady cycle life (93% after 100 cycles). Such outstanding performance is paired with features appropriate for large-scale industrial production of silicon batteries, such as active mass loading of at least 3.9 mg cm−2, a high-tap density electrode material of 1.68 g cm−3 (secondary clusters: 1.12 g cm−3), and a production yield of up to 1 kg per day.

Glucose intolerance in acromegaly is driven by low insulin secretion; results from an intravenous glucose tolerance test.

Insulin sensitivity (Si) and its role in glucose intolerance of acromegaly has been extensively evaluated. However, data on insulin secretion is limited. We aimed to assess stimulated insulin secretion using an intravenous glucose tolerance test (IVGTT) in active acromegaly. We performed an IVGTT in 25 patients with active acromegaly (13 normal glucose tolerance [NGT], 6 impaired glucose tolerance [IGT] and 6 diabetes mellitus [DM]) and 23 controls (8 lean NGT, 8 obese NGT and 7 obese IGT). Serum glucose and insulin were measured at 20 time points along the test to calculate Si and acute insulin response (AIRg). Medical treatment for acromegaly or diabetes was not allowed. In acromegaly, patients with NGT had significantly (p for trend < 0.001) higher AIRg (3383 ± 1082 pmol*min/L) than IGT (1215 ± 1069) and DM (506 ± 600). AIRg was higher in NGT (4764 ± 1180 pmol*min/L) and IGT (3183 ± 3261) controls with obesity than NGT (p = 0.01) or IGT (p = 0.17) acromegaly. Si was not significantly lower in IGT (0.68 [0.37, 0.88] 106*L/pmol*min) and DM (0.60 [0.42, 0.84]) than in NGT (0.81 [0.58, 1.55]) patients with acromegaly. NGT (0.33 [0.30, 0.47] 106*L/pmol*min) and IGT (0.37 [0.21, 0.66]) controls with obesity had lower Si than NGT (p = 0.001) and IGT (p = 0.43) acromegaly. We demonstrated that low insulin secretion is the main driver behind glucose intolerance in acromegaly. Compared to NGT and IGT controls with obesity, patients with NGT or IGT acromegaly had higher Si. Together, these findings suggest that impaired insulin secretion might be a specific mechanism for glucose intolerance in acromegaly.

Investigating the mechanism of formation of Ca-rich Ca[sbnd]Yb apatite that forms from the Yb-silicate–CMAS reaction at 1300°C

The formation mechanism and structure of Ca-rich CaYb apatite, which forms from the corrosion of Yb-silicate based coatings with CMAS at 1300°C in air for 48 h was investigated. X-ray photoelectron spectroscopy (XPS) was used to determine the bond type and oxidation states of the apatite. XPS data showed that the Si2p peaks are related to silicates, while the Ca2p and Yb4d are linked to apatite structures. The mechanism of growth for the apatite is proposed using the Wagner-Hauffe oxidation principle and the Kröger-Vink notations. The formation mechanism of the apatite-structure reaction phase is by substitutional diffusion, which is governed by the movement (formation and destruction) of point defects within the Yb2O3 lattice, particularly oxygen vacancies and electron holes. When Ca2+ substitutes Yb3+ in its lattice position, this results in the formation of anionic vacancies, which leads to more Ca2+ diffusion. The diffusion process continues until vacancies can no longer form to achieve electroneutrality, which leads to the newly formed Yb–Ca–Si being saturated with cations. Thus, based on this investigation, it is assumed that a CaYb silicate oxyapatite coatings can suppress the vacancy formation mechanism by containing high Ca and Si content which can thus decrease the ionic diffusion from CMAS melt into the EBC lattice. This can be the premises of a more CMAS-resistant coating family.

Synergistic effect mechanism of biomass ash-derived K-Ca-Si catalytic system on syngas production and reactivity characteristics of high-sulfur petroleum coke gasification

In this study, three typical biomass ash (BA) components, KCl, CaCO3 and SiO2, are selected as model compounds to construct BA-based key ternary component system for petroleum coke (PC) gasification. Gas product analysis was conducted using gas chromatography to study the influence of different catalysts on the gas product distribution, gas yield and carbon conversion of PC gasification, and clarify the synergistic effects of binary and ternary components in K-Ca-Si catalytic system. In addition, electron scanning microscopy (SEM) and Raman techniques are used to characterize the physicochemical structure of gasification semi-char to reveal the synergistic mechanism of K-Ca-Si system. The results show that the yield of different gases is ordered as H2 > CO > CO2 and the increment of H2 yield, CO yield, syngas yield and carbon conversion in K-Ca-Si catalytic system is 43.41 mmol/g, 26.67 mmol/g, 80.37 mmol/g and 0.49, compared with single PC gasification, respectively. By comparing the theoretical and actual value of gas yield and carbon conversion, it is found that there are synergistic catalytic effects for K-Ca-Si ternary catalyst, but Si will inhibit the activity of K and Ca. Coupled with SEM and Raman analysis, synergistic mechanism of ternary catalytic system can be revealed. KCl and CaCO3 reduce the graphitization degree of semi-char by reacting with carbon matrix, and CaCO3 can stimulate the pore structure development of semi-char, which accelerate reaction between KCl and carbon matrix to form intermediate active sites, thus favoring gasification reaction and exhibiting a synergistic effect. SiO2, on the other hand, will combine with KCl and CaCO3 to form inert silicates, resulting in the deactivation of KCl and CaCO3. It could be concluded that for high K-high Ca-low Si ternary catalytic system, KCl and CaCO3 would still show a synergistic effect due to higher CaCO3 content than SiO2.

Hydrothermal transformation of fly ash to tobermorite or katoite: Impact of Ca and Si concentration in the liquid phase without alkali activation

In the study of hydrothermal conversion of fly ash to calcium silicate hydrates (C–S–H), the concentration of Ca and Si in the liquid phase plays a vital role in determining the hydrothermal transformation results. This paper selected a fly ash as a research object, which can leach a high Si concentration into the solution in the hydrothermal process even in a slight alkaline solution, based on a new finding when studying the alkali dissolution kinetics of different fly ashes. To explore the effects of Ca and Si concentrations in the liquid phase on the hydrothermal transformation of fly ash to tobermorite or katoite, Na2SiO3 (Na2O·xSiO2·yH2O) and CaSO4 were used to change the concentration of Si and Ca in the liquid in the hydrothermal system. Characterization methods such as XRD, SEM, infrared spectroscopy, and solid-state nuclear magnetic resonance indicated that a little more concentration of Si can promote the transformation from fly ash to tobermorite and persuade the conversion of the Si–O tetrahedron in C–S–H from Q2 to Q3 and Q4. However, too high a liquid Si concentration made the hydrothermal product change to colloidal calcium silicate. On the other hand, a high Ca concentration in the liquid was found to lead to the conversion of the hydrothermal product from tobermorite to katoite. According to the above results, the deep transformation from fly ash to tobermorite under the conditions of a low temperature of 160 °C and no extra alkali addition was achieved by the induction of a small quantity of Na2SiO3.

Nanocellulose-Based Ecofriendly Nanocomposite for Effective Wastewater Remediation: A Study on Its Process Optimization, Improved Swelling, Adsorption, and Thermal and Mechanical Behavior.

A nanocellulose (NC)-based cross-linked adsorbent has been employed herein for the removal of dye pollutants (e.g., methylene blue) from the textile industry. The synthesized hydrogel was optimized to achieve the best concentrations of the adsorbent constituents, i.e., 1.55% guar gum, 1.46% NC, and 0.84% borax for achieving the maximum swelling index (SI, 3741.42%) and higher adsorption capacity (qe, 24.05 mg g-1). 98.8% of dye qe was achieved at optimal conditions of pH 8 within 30 min at 30 °C. Adsorption isotherms and kinetics investigations showed good correlation with the Freundlich adsorption isotherm model (R2 > 0.9889; ΔG° = -4.71; ΔH° = -12.30; ΔS° = -0.025) as well as the pseudo-second-order kinetics model, indicating multilayered and intricate adsorption mechanisms for dye removal. The study of thermodynamic parameters confirmed the exothermic nature of the adsorption process. The adsorption-desorption study of the resulting hydrogel exhibited 64.58% dye removal efficiency even after 4 consecutive cycles of reuse. Further, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction analysis revealed the surface morphology, functional moieties, thermal behavior, and crystallinity pattern of the hydrogel. Rheological analysis demonstrated pseudoplastic flow and improved mechanical behavior for the hydrogel. The current study found that the synthesized adsorbent with a higher SI and qe has a noticeable potential for the removal of dye pollutants from wastewater.

From 0D to 3D: Hierarchical structured high-performance free-standing silicon anodes based on binder-induced topological network architecture

Free-standing silicon anodes with high proportion of active materials have aroused great attention; however, the mechanical stability and electrochemical performance are severely suppressed. Herein, to resolve the appeal issues, a free-standing anode with a “corrugated paper” shape on micro-scale and a topological crosslinking network on the submicron and nano-scale is designed. Essentially, an integrated three-dimensional electrode structure is constructed based on robust carbon nanotubes network with firmly anchored SiNPs via forming interlocking junctions. In which, the hierarchical interlocking structure is achieved by directional induction of the binder, which ensures well integration during cycling so that significantly enhances mechanical stability as well as electronic and ionic conductivity of electrodes. Benefiting from it, this anode exhibits outstanding performance under harsh service conditions including high Si loading, ultrahigh areal capacity (33.2 mA h cm−2), and high/low temperatures (−15–60 °C), which significantly extends its practical prospect. Furthermore, the optimization mechanism of this electrode is explored to verify the crack-healing and structure-integration maintaining along cycling via a unique self-stabilization process. Thus, from both the fundamental and engineering views, this strategy offers a promising path to produce high-performance free-standing electrodes for flexible device applications especially facing volume effect challenges.