Low Si Research Articles

Indosinian magmatism and mineralization in the Banjiaoyuan tin deposit, middle Nanling Range, South China: Constraints from zircon and cassiterite U-Pb ages, geochemistry and Sr-Nd-Hf isotopic compositions

Indosinian W-Sn metallogeny associated with granites in South China has been reported in recent years by many researchers. However, the refined genetic relations between these deposits and the related granites remain unclear in most areas, and the tectonic setting of Indosinian magmatism and W-Sn mineralization are still widely controversial. The Banjiaoyuan tin deposit is located in the east vicinity of Yangmingshan pluton in the middle Nanling Range, South China. The granitic stocks in this deposit comprise two intrusive episodes, i.e., the first episode of medium-coarse-grained porphyritic tourmaline-biotite monzogranite (G1), and the second episode of micron-fine-grained tourmaline-muscovite monzogranite (G2). LA-ICP-MS zircon U-Pb dating gives weighted ages of 226.9 ± 1.6 Ma to 223.8 ± 1.9 Ma for G1, and 224.3 ± 2.0 Ma for G2, respectively. LA-MC-ICP-MS cassiterite U-Pb dating yields Tera-Wasserburg concordia age of 216.7 ± 2.4 Ma for tin mineralization. These ages indicate that both the granitic magmatism and related mineralization were initiated in the late Indosinian period. All the granites have high SiO2, Al2O3, P2O5 contents, and low TFeO, CaO, MgO, TiO2 contents, indicating that the granites are highly differentiated S-type granites, and furthermore, the high DI and Rb, K, U, Hf, Sm, low SI and Ba, Sr, Ti, TREE further show that the granites have undergone high extent of differentiation and evolution. High Rb/Nb and K/Nb ratios, low Nb/Ta and Zr/Hf ratios, widely varying CaO/Na2O ratios, low and uniform εNd(t) values, and dominantly negative and relatively dispersed εHf(t) values jointly indicate that the granites were derived from a heterogeneous mixture of calcium-poor mudstone and calcium-rich psammite (or metamorphic igneous rocks) in the crust. The known Indosinian W-Sn deposits in South China are more closely related to S-type granites than to I-type granites, suggesting that their ore-forming materials are mainly derived from the crust. In addition, individual positive εHf(t) values indicate that a small amount of newborn crustal components were involved in the formation of granitic magma. Compared with G1, G2 differs distinctly in petrological, chemical and isotopic characteristics, especially it is more richer in F content and contains magmatic cassiterite and wolframite crystals, suggesting that G2 have undergone higher extent of differentiation and evolution, and are much more closely related to the Sn-W mineralization than G1. The late Indosinian granites in this deposit were formed in post-collisional extensional tectonic environment, while the early Indosinian granites intruded in the Yangmingshan area were formed in syn-collision compression environment. Based on the statistics, the metallogenic ages of Indosinian W-Sn deposits in South China are between 212 and 230 Ma, and the petrogenetic ages of related granites are between 211 and 230 Ma, both age groups belong to the late Indosinian period, representing a regional large-scale granitic magma intrusion and mineralization event that initiated in post-collisional extensional tectonic environment.

Vertical sidewall of silicon nitride mask and smooth surface of etched-silicon simultaneously obtained using CHF3/O2 inductively coupled plasma

Silicon nitride (SiNx) has been playing a vital role in the fabrication of micro- and nano-scale structures in numerous applications for several decades. Optimal etch recipes and a mechanistic understanding of the SiNx plasma-etching process are necessary for its adoption as a hard mask. We present a systematic investigation on SiNx films and underlying silicon (Si) plasma etching via an inductively coupled plasma (ICP) system using a CHF3/O2 mixture. Effects of ICP power, RF power, CHF3 flow rate on SiNx etching rate, CHF3/O2 gas ratio on SiNx sidewall profile, Si surface roughness, and SiNx/Si etching selectivity have been methodically investigated. We paid particular attention to studying the effect of O2 concentration on SiNx and Si etching mechanisms. It was found that SiNx sidewall profile, Si surface roughness, and SiNx/Si etching selectivity depend strongly on the O2 concentration. A nearly vertical SiNx sidewall of 89°, a low Si surface roughness of 0.2 nm, and a high SiNx/Si etching selectivity of 2 were simultaneously achieved by adjusting O2 concentration to 10% with CHF3+O2 total flow rate of 50 sccm. Finally, the composition of the residue on the surface of the processed sample was examined by X-ray photoelectron spectroscopy (XPS).

PMON244 Alterations in Nonesterified Free Fatty Acids (NEFA) Trafficking Rather Than Hyperandrogenism Contribute to Variations in Insulin Sensitivity Among Obese Women with Polycystic Ovary Syndrome

Abstract Objectives To compare the metabolic and hormonal features of metabolically unhealthy obese PCOS women (MU-PCOS) vs. metabolically healthy obese PCOS women (MH-PCOS) and determine whether alterations in non-esterified free fatty acids (NEFA) response to hyperinsulinemia contribute to variations in insulin sensitivity between MU-PCOS and MH-PCOS. Design Prospective cross-sectional study. Setting Tertiary-care academic center. Methods Insulin resistance (IR) in the basal state was assessed by HOMA-IR in 125 consecutive obese oligo-ovulatory PCOS women (BMI≥ 30 kg/m2; NIH 1990 or Rotterdam 2003 Phenotype A/B) undergoing an oral glucose tolerance test (oGTT); and IR in the dynamic state assessed by the modified frequently sampled intravenous glucose tolerance test (mFSIVGTT) in a subgroup of 16 non-diabetic obese PCOS women. Main Outcome Measures: Primary outcome measures were: 1) IR in AT was assessed in the basal state by the Adipose Insulin Resistance Index [Adipo-IR]) and dynamically by the mFSIVGTT-derived indices of insulin-mediated NEFA suppression [NEFAnadir, TIMEnadir, and %NEFAsupp]); 2) peak lipolysis rate [SNEFA]; and 3) peak NEFA uptake rate [KNEFA]. Secondary outcome measures were levels of insulin and glucose during oGTT, HOMA-β%, and degree of hyperandrogenism (i.e. mF-G score, free testosterone [T], total T, DHEAS). Results Eighty-five obese PCOS participants undergoing oGTT had a HOMA-IR index of ≥2.5 (MU-PCOS) and 40 had a HOMA-IR of <2.5 (MH-PCOS). MU-PCOS had higher mean HOMA-β%, levels of fasting, 1-hr and 2-hr. glucose and insulin, and peak insulin during the oGTT, and higher prevalence of prediabetes and elevated 1-hr. glucose and a trend towards higher prevalence of type 2 diabetes mellitus (T2DM), than MH-PCOS. Alternatively, measures of HA were similar between the groups. Assessing IR dynamically, subjects were subdivided into MU-PCOS by an insulin sensitivity index [Si] ≤1.7 [mU/L]−1·min−1 (n=8) or MH-PCOS by an Si ≥5.6 [mU/L]−1·min−1 (n=8), matched for age and BMI. MU-PCOS had lower Si and KNEFA, smaller %NEFAsupp, longer TIMEnidar, and higher NEFAnidar and Adipo-IR than MH-PCOS, although fasting plasma NEFA levels and SNEFA were similar. In bivalent analysis, Si correlated strongly and negatively with NEFAnadir, weakly and negatively with TIMEnadir, and positively and strongly with KNEFA and NEFAsupp, in MUO-PCOS only. Conclusion Independent of age and BMI, metabolically unhealthy obese PCOS women, compared with metabolically healthy obese PCOS women, had lower rates of NEFA uptake and altered insulin-mediated plasma NEFA suppression in response to mFSIVGTT-determined endogenous insulin secretion, rather than disparities in HA and rate of lipolysis, mechanism that may contribute to variations in insulin sensitivity among obese PCOS women. Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.

Soft X-Ray Spectral Diagnostics of Multithermal Plasma in Solar Flares with Chandrayaan-2 XSM

Spectroscopic observations in X-ray wavelengths provide excellent diagnostics of the temperature distribution in solar flare plasma. The Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission provides broadband disk-integrated soft X-ray solar spectral measurements in the energy range of 1–15 keV with high spectral resolution and time cadence. In this study, we analyze the X-ray spectra of three representative GOES C-class flares obtained with the XSM to investigate the evolution of various plasma parameters during the course of the flares. Using the soft X-ray spectra consisting of the continuum and well-resolved line complexes of major elements like Mg, Si, and Fe, we investigate the validity of the isothermal and multithermal assumptions on the high-temperature components of the flaring plasma. We show that the soft X-ray spectra during the impulsive phase of the high-intensity flares are inconsistent with isothermal models and are best fitted with double-peaked differential emission measure distributions where the temperature of the hotter component rises faster than that of the cooler component. The two distinct temperature components observed in differential emission measure models during the impulsive phase of the flares suggest the presence of the directly heated plasma in the corona and evaporated plasma from the chromospheric footpoints. We also find that the abundances of low first ionization potential elements Mg, Si, and Fe reduce from near coronal to near photospheric values during the rising phase of the flare and recover back to coronal values during the decay phase, which is also consistent with the chromospheric evaporation scenario.

Study on the behavior of impurities in zone melting of aluminum

In this study, the migration and distribution behaviors of Cu, Si, Fe, and Ti impurities in the process of preparing high-purity Al by zone melting under an argon atmosphere were investigated. The width of the molten zone during the experiment was determined as 40 mm, based on simulation calculation results. The influences of the travel speed of the molten area and number of zone melting times on the migration and distribution of the Cu, Si, Fe, and Ti impurities in the Al were experimentally demonstrated. The contents of the impurities Cu, Si, Fe, and Ti in the middle of the sample (i.e., 140 mm from the head end) were 0.9057, 0.8116, 0.1202, and 0.4237 ppm, respectively, when the travel speed of the molten area was 1.0 mm/min and with 15 times of zone melting. The contents of all the above impurities were reduced to the requirements of Chinese national standard and 99.9995% (i.e., 5N5) high-purity Al was obtained from 4 N Al by the zone melting method under the above optimal experimental conditions. The experimental results show that the effect of the number of zone melting times on the removal of the Cu, Si, and Fe impurities is more evident, and that these impurities are easier to separate than Ti. Therefore, high-purity Al with lower Cu, Si, and Fe contents can be obtained by optimizing the travel speed of the molten area and number of zone melting times.

Structure and phase constitution of graphite-loaded reaction-bonded sic

The influence of porous SiC preforms densities for the siliconizing process on the structure and phase constitution of graphite-loaded reaction-bonded SiC (G-SiSiC) was studied. It was found that varying the densities of porous SiC preforms containing artificial graphite of similar grain size with the dimensions less than 25 mm (in height or diameter) can lead to the G-SiSiC samples with low free Si content (less 4 wt.%.). It was also shown that reaction sintering of G-SiSiC samples with the optimized densities during the siliconizing process results in the formation of a dense fine-grained SiC layer. Moreover, during the siliconizing process, a dense SiC gradient matrix is formed in which graphite and Si inclusions are uniformly dispersed in bulk.

Influence of the interaction between Si and Sc on the microstructure and tensile properties of as casted Al-Si-Sc alloys

Scandium (Sc) and silicon (Si) are effective for modifying Al based alloys, while their combined effect may be limited by some Si-Sc interaction, which was rarely reported. In this work, Al alloys with varying Si and Sc additions were prepared for microstructure characterization and tensile testing. The results show that Sc refines the α-Al grain via a heterogeneous nucleation induced by in-situ formed primary Al3Sc. A network AlSi2Sc2 phase was formed via a eutectic reaction and a bulk AlSi2Sc2 was generated from a peritectic reaction. Both AlSi2Sc2 competitively consumed the Sc solute in the same alloy, weakening the refining effectiveness of Al3Sc. The Sc also refined the eutectic Si to more ordered fiber/plate-like structure, and a proper ratio of Si to Sc could avoid the AlSi2Sc2 formation. When increasing Sc from 0.3 to 1.0 wt% in Al alloys containing 6 wt% Si, the ultimate tensile strength (UTS) and yield strength (YS) increased, but the EL decreased due to the presence of AlSi2Sc2 phase. The UTS and YS can increase along with a 41% raise in EL by a strategy combining higher Sc (>0.6 wt%) and a lower Si (<4 wt%) with Al3Sc in a dominant role in solidification reactions without AlSi2Sc2 formation. The mechanisms of microstructure modification with Si-Sc interaction are also discussed.

Facile synthesis of yolk-shell Si@void@C nanoparticles with 3D conducting networks as free-standing anodes in lithium-ion batteries

The low cost and high performance via a simple way of fabrication are considerable challenges for Si-based anode in the application of lithium-ion batteries. In this study, we synthesize a novel free-standing Si/C anode, consisting of yolk (Si)-shell (amorphous carbon) nanoparticles and carbon nanofibers (denoted as Si@void@C/CNFs), via a facile route of template removal and electrospun. The designed yolk-shell structure help buffer the volume expansion of silicon during the discharge/charge cycles, and the intertwined CNFs are conducive to electron fast transmission and guarantee structural integrity. As expected, with a low Si content (∼23 wt%), the self-supporting electrode of Si@void@C/CNFs exhibits a high specific capacity of ∼627.5 mAh g−1 as well as 69.3% capacity retention at 0.1 A g−1 after 100 cycles, better than Si@C/CNFs (20%) and Si/CNFs (9.5%) electrodes. The superior performance of Si@void@C/CNFs indicates that it is an attractive anode material for the practical application of Lithium-ion batteries.

(Digital Presentation) Properties of Selectively Grown Si:P Layers below 500°C for Use in Stacked Nanosheet Devices

With the introduction of novel stacked CMOS transistor integration schemes such as sequential 3D and CFETs [1,2], there is an increasing need for highly active source/drain layers with a low overall thermal budget. For some integration schemes, processing temperatures below ~ 525°C are desired [3] and in most cases, the contacts need to be formed on the {110} surfaces of exposed Si nanosheets. In this paper, we report on selectively grown Si:P layers below 500°C targeting application in stacked nanosheet-based devices. In contrast to conventional approaches where selectivity is obtained at low temperatures using Cyclic-Deposition and Etch (CDE) with HCl/GeH4 as an etchant [4,5], we rely for this work on Cl2-based etching in combination with Si3H8 as a high-order Si precursor [6]. The Si:P layers were grown in a 300 mm ASM Intrepid® ES reduced pressure chemical vapor deposition reactor on Si (001) substrates.Figure 1 shows some typical characteristics for the Si:P layers without etching (“Dep-only”) and CDE Si:P layers below 500°C. As the temperature is lowered, the growth rate and P incorporation for a given PH3 flow decreases substantially, while the active concentration increases. For both the “Dep-only” and CDE layers, a minimum develops in the resistivity which corresponds to a maximum in active concentration as derived from micro-Hall measurements. Due to the etching during CDE, a P-enrichment takes place and the P concentration in the layers is enhanced compared to the “Dep-only” case. A minimum resistivity of 0.28 mOhm.cm (Pact ~ 6e20/cm3) is obtained for CDE at 480°C which is slightly larger than the minimum resistivity of 0.24 mOhm.cm (Pact ~ 1e21/cm3) for the “Dep-only” case at the corresponding temperature.Figure 2 shows the application of the CDE process on wafers with fins. By lowering the deposition time at a constant etching time per cycle, a (wafer-scale) selective regime can be reached. For the “Dep-only” case, quite some defects and nuclei are present on the sidewalls of the Si-fins and the oxide dielectric, respectively, which are finally removed by sufficient Cl2 etching.Figure 3 compares the corresponding X-TEMs of the above fins after “Dep-only” and selective CDE conditions. For the “Dep-only” case we can only observe a mono-crystalline growth in the <100> direction. For other growth directions like <110>, epitaxial breakdown-down occurs resulting in a substantially reduced crystalline thickness. With the use of Cl2 based CDE, a selective growth can be reached as well as a clear structural improvement in the <110> growth direction, which is very important for the application in nanosheet devices. Finally, once a (111) facet is formed, twin defects occur as expected for low temperature Si:P and Si:C:P [7].The growth behavior of the CDE processes in relevant nanosheet geometries is currently under investigation.

Green Silicon Carbide (SiC) and SiC/Graphite Composite Anodes for Lithium-Ion Batteries

Arising from concerns of continuously deteriorating environmental issues, worldwide efforts are dedicated to developing more sophisticated energy storage techniques to replace traditional nonrenewable sources. Given the significant greenhouse gas emissions that occur coincident with current battery production and operation, the introduction of agricultural waste rice hull ash (RHA), a byproduct of biomass combustion, as a source for battery components could facilitate the actual realization of green and sustainable energy storage. Herein, we focus on using RHA to produce SiC with hard carbon (HC) nanocomposites and their mixtures with graphite as Li+ battery anodes.Using a simple method developed in our laboratories to control SiO2:HC ratios, the intrinsic nanoscale mixing of SiO2 and HC in RHA provides a natural starting material for carbothermal reduction producing high purity SiC without the need to add an external carbon source. The optimized SiC/HC nanocomposites contain ≈13 wt. % HC, showing BET surface areas >200 m2/g.We previously reported the SiC/HC nanocomposites derived from RHA exhibit charge/discharge capacities 3× of current graphite anodes at > 950 mAh g-1, accompanied by distinct capacity increases. In particular, SiC can be lithiated to Li1.1-1.4SiC without forming LixSi or LixC. Investigations of the lithiation/delithiation mechanisms using multiple techniques coupled with modeling suggest a cubic (3C-SiC) to hexagonal phase transition (6H-SiC) after long-term cycling, which may explain the origins of extraordinary capacity increments. Moreover, lithiation/delithiation occur without significant volume changes according to XRD and SEM, suggesting that SiC can compete with metallic Si as an anode material as free volumes equivalent to 3× the charged Si are required.Most recently, inspired by the developed concept of adding graphite to improve the performance of silicon-based anodes, we find adding graphite to SiC/HC nanocomposites results in a 3× improvement in capacity increases on cycling, reaching >950 mAh g-1 after 150 cycles. The proposed interactions within the composites will also be addressed in this presentation. It should be noted most silicon/graphite composite anodes use low Si contents of < 30 wt. % to limit the total electrode volume expansion and ensure contacts and conductivities between components, which restrains the practical energy density improvements from using Si in the anodes. In comparison, mixing only 30 wt. % graphite with SiC/HC in the current work results in specific capacities competitive with Si. Furthermore, Si metal can be synthesized via the carbothermal reduction at ≈1900 °C, while battery-grade graphite used today is produced in an environmentally harmful and expensive multistep method that involves heating to ≈3000 °C. The SiC/HC need only be heated to 1450 °C, with hard carbon forming coincidentally providing positive effects on anode performance. In this aspect, directly using SiC/HC or adding a low amount of graphite to further boosts its performance in an apparently more environmentally friendly route to alternative anodes.

(Digital Presentation) Application of Polarity Reversal and Performance Analysis of Continuous Electrocoagulation

An important challenge for continuous treatment by electrocoagulation (EC) is the passivation and fouling of electrodes which increases during the longer operation (Ingelsson et al., 2020). The application of polarity reversal (PR) and treatment performance of EC was investigated using continuous flow reactor for simultaneous removal of silica and hardness (calcium and magnesium) from produced water. Polarity reversal times (PRT) from 30 s to 10 min were studied at a fixed charge loading of 2000 C L- 1 (i.e., the amount of charge passed per unit volume of produced water treated) using Fe and Al electrodes. Periodic PR was found to reduce the fouling and de-passivate the electrodes by changing the surface chemistry at the electrode-electrolyte interface (Ingelsson et al., 2020; Yasri et al., 2022). During 90 minutes of continuous treatment the chronopotentiometric data indicated that a PRT of 10 min was more effective in reducing the cell voltage for both Fe and Al electrodes [Fig. 1 (a & b)]. With a longer PRT of 10 min, there is more time for the acid boundary layer to form on the anode, which mitigates metal precipitation at the anode. In contrast the higher cell voltage that persists in direct current EC (DC-EC) could be due to the precipitation of Ca and Mg minerals in the alkaline solution on the cathode surface, leading to cathode passivation (Chow et al., 2021). After the first polarity reversal, both electrodes have been anodic, removing passivation layers from the surface and reducing the cell voltage. On reversing the polarity, the cathode becomes the anode, and the acidic pH on the formed at the electrode interface will facilitate the dissolution of Ca and Mg precipitates on the electrode surface, reducing the cell voltage significantly. For Fe-EC, the contaminant removal performance increased with PRT, and the highest removal was observed with DC-EC (Fig. 1c). The increasing removal performance with PRT for Fe-EC is consistent with the increase in faradaic efficiency observed of 55%, 68%, 85%, and 99.8% with 30 sec, 2 min and 10 min PRT, and DC respectively. The lower faradaic efficiencies for Fe-EC with short PRTs are likely due to redox reactions of iron species at the electrode surface (Chow et al. 2021).The contaminant removal at a charge loading of 2000 C L–1 using DC-EC with Al electrodes was similar to that for PR-EC with PRTs of 2 to 10 min (Fig. 1d). Slightly lower Si and hardness removal was observed for Al-EC at the shortest PRT of 30 s. For Al-EC, the faradaic efficiency was also observed to increase with PRT, with values of 150%, 220% and 287% obtained at 30 sec, 2 min and 10 min PRT respectively. The super-faradaic (>100%) efficiencies can be explained by dissolution of the Al from the cathode under the local alkaline conditions that develop on the electrode surface. With a short PRT, there is less time for the alkaline pH to develop at the surface and hence the faradaic efficiency was reduced.

High-temperature thermal stability of C/C-ZrC-SiC composites via region labeling method

To investigate the thermal stability of ceramic-matrix composites, three kinds of C/C-ZrC-SiC composites with different Zr/Si molar ratios were synthesized by reactive melt infiltration. Employing region labeling method, the high-temperature thermal stability of the composites was systematically studied by changing the temperature and holding time of thermal treatment. Results show that the mass loss rate of low Si composites has a growth trend with increasing temperature, and a crystal transformation from β-SiC to α-SiC occurs in the composites. In the calibrated area, SiC phase experiences Ostwald ripening and volume change with location migration, while ZrC phase experiences a re-sintering process with diffusion. Moreover, it is found that increasing temperature has a more obvious effect on the thermal stability than extending holding time, which is mainly attributed to the faster diffusion rate of atoms.

Fluid Pressure Changes Recorded by Trace Elements in Quartz

AbstractFluid pressure is a key parameter in earthquake mechanics, controlling seismic failure and plate coupling in convergent zones. Yet fluid pressure is also extremely difficult to quantify at seismogenic depth, which limits our knowledge of the stress state in accretionary prisms. Here, we show that the geochemical record of exhumed hydrothermal quartz veins may be used to place quantitative bounds on fluid pressure variations in subduction zones. The studied veins come from sediments accreted and exhumed by plate convergence in southwestern Japan. Quartz in veins displays growth rims of contrasted bright blue/dark brown cathodoluminescence (CL) colors, high/low Al concentrations, and low/high fluid inclusion abundance. Because Si‐Al substitution (and charge compensation by Li) strongly depends on the rate of quartz precipitation and Si solubility, Al‐Li concentrations must be sensitive to fluid pressure. This is confirmed by fluid inclusions, the density of which, converted into trapping pressures, record fluid pressure drops by up to ∼70 MPa from CL‐brown, Al‐Li‐poor rims to CL‐blue, Al‐Li‐rich quartz rims. CL‐blue rims grow at a fast rate, high Si supersaturation and low fluid pressure whereas CL‐brown rims grow at a slower pace, lower Si supersaturation, and higher fluid pressure. Quartz trace element chemistry thus offers a promising tool to quantify deep fluid pressure variations and their relationships to earthquakes.

Silicon as a potential limiting factor for phosphorus availability in paddy soils

Rice cultivation requires high amounts of phosphorus (P). However, significant amounts of P fertilizer additions may be retained by iron (Fe) oxides and are thus unavailable for plants. At the same time, rice cultivation has a high demand for silicic acid (Si), reducing Si availability after short duration of rice cultivation. By studying a paddy chronosequence with rice cultivation up to 2000 years, we show that Si limitation, observed as early as a few decades of rice cultivation, is limiting P availability along the paddy soils chronosequence. Using near edge X-ray absorption fine structure spectroscopy (NEXAFS) in a scanning transmission (soft) X-ray microscope (STXM) we show release of available P was linked to a Si-induced change in speciation of Fe-phases in soil particles and competition of Si with P for binding sites. Hence, low Si availability is limiting P availability in paddy soils. We propose that proper management of Si availability is a promising tool to improve the P supply of paddy plants.

Coupling Molecular-Scale Spectroscopy with Stable Isotope Analyses to Investigate the Effect of Si on the Mechanisms of Zn-Al LDH Formation on Al Oxide.

While silicate has been known to affect metal sorption on mineral surfaces, the mechanisms remain poorly understood. We investigated the effects of silicate on Zn sorption onto Al oxide at pH 7.5 and elucidated the mechanisms using a combination of X-ray absorption fine structure (XAFS) spectroscopy, Zn stable isotope analysis, and scanning transmission electron microscopy (STEM). XAFS analysis revealed that Zn-Al layered double hydroxide (LDH) precipitates were formed in the absence of silicate or at low Si concentrations (≤0.4 mM), whereas the formation of Zn-Al LDH was inhibited at high silicate concentrations (≥0.64 mM) due to surface-induced Si oligomerization. Significant Zn isotope fractionation (Δ66Znsorbed-aqueous = 0.63 ± 0.03‰) was determined at silicate concentrations ≥0.64 mM, larger than that induced by sorption of Zn on Al oxide (0.47 ± 0.03‰) but closer to that caused by Zn bonding to the surface of Si oxides (0.60-0.94‰), suggesting a presence of Zn-Si bonding environment. STEM showed that the sorbed silicates had a close spatial coupling with γ-Al2O3, indicating that >Si-Zn inner-sphere complexes (">" denotes surface) likely bond to the γ-Al2O3 surface to form >Al-Si-Zn ternary inner-sphere complexes. This study not only demonstrates that dissolved silicate in the natural environment plays an important role in the fate and bioavailability of Zn but also highlights the potential of coupled spectroscopic and isotopic methods in probing complex environmental processes.

Observation and Mitigation of Lamellar Silica Particles Formed in Pharmaceutical Products Packaged in Glass Vials

A new type of lamellae-like particles was observed in protein based liquid therapeutic protein drug product (DP) packaged in standard (STD) and delamination controlled (DC) Type IB glass vials stored at 2-8°C as early as two weeks after manufacture. These particles were determined to be remarkably different from lamellae in not only in their chemical composition, but in the mechanism by which these are formed. The lamellae-like particles were an ultra-thin (< 200 nm) film, appeared curled, sheet-like, folded with no defined edges identified as lamellar silica composed of silica and polysorbate 80 (PS 80). It was also observed that the lamellar silica particles, when formed in a given drug product lot, not only were observed in a small percentage of vials, but also remained at low (≤ 5) numbers in affected vials, often decreasing in number over time. This is in contrast to the large number of commonly reported glass lamellae (hundreds per vial) observed in vials prone to delamination with a glass vial interior showing a delaminated inner surface. In this case study, evidence from low Si leachable levels in solution and various surface analytical techniques supported the conclusion that there was neither delamination nor early signs of glass delamination like reaction zones occurring in those impacted vials, regardless. A mechanism for particle formation was hypothesized and experimentally confirmed. Lamellar silica particles are composed of an admixture of condensed silica and PS 80 deposited on the interior walls of glass vials, which form and may be released into solution over time. The root cause was determined to be conditions present during preparation of the vials for drug product filling, specifically the vial washing and depyrogenation steps. These conditions are known to make glass vials prone to delamination; in this case study, they resulted in interactions between the glass and PS 80 present in the formulation. Incomplete drying of the glass vials during depyrogenation in closed ovens was confirmed as the contributing factors that led to lamellar silica particle formation via the studies of silicate spiked into the DC Type IB glass vials filled with the mAb DP in which lamellar silica particles were observed. Prevention of lamellar silica particles formation was successfully achieved through optimization of the duration and pressure of air blow during the vial washing and drying process in a depyrogenation oven. This was evidenced by the lack of appearance of the lamellar silica particles over 48 months for the DP lots filled post optimization. Additionally, the formation of lamellar silica was also mitigated by changing the vial washing process from a closed oven process to a tunnel process, which allowed for improved air flow and hence better drying of the vial primary container.

Non-equilibrium BaxSr1-xSO4 solid solution compositions at elevated Sr2+ concentration, ionic strength, and temperature

The BaxSr1-xSO4 solid solution is ubiquitously present in both geological and industrial processes, where they mostly form under non-equilibrium conditions. Compared with those formed under equilibrium conditions, the BaxSr1-xSO4 solid solution formed at non-equilibrium condition has significantly higher Sr incorporation at the same aqueous phase compositions. The solid composition of BaxSr1-xSO4 formed at non-equilibrium condition is critical for the study of chemical palaeoceanography as well as the solid solution nucleation and growth kinetics. However, few studies have been conducted to investigate the composition of the BaxSr1-xSO4 solid solution when it precipitates at non-equilibrium conditions. In this study, the distribution coefficient of Ba2+ and Sr2+ between the BaxSr1-xSO4 solid solution and the aqueous phases (KD,Sr-Barite) at non-equilibrium conditions was studied with barite saturation index (SIbarite) from 0.9 to 1.5, [Sr2+]/[Ba2+] molality ratio from 0.33 to 30, temperature (T) from 50 to 90 °C and ionic strength (IS) from 0.01 M to 3 M as NaCl, with celestite being undersaturated. The composition of the BaxSr1-xSO4 solid solution formed at non-equilibrium conditions can then be calculated from the KD,Sr-Barite values. The results show that the KD,Sr-Barite value decreases with the increase of aqueous Sr2+ concentration at fixed SIbarite and T conditions. The IS effect on the KD,Sr-Barite value is small. Based on the experimental results, a new empirical model is developed to accurately predict the measured compositions of BaxSr1-xSO4 solid solution at non-equilibrium conditions under a wide T and IS conditions as follows (the plot of the predicted log10KD,Sr-Barite versus the measured log10KD,Sr-Barite with R2=0.9995):KD,Sr-Barite=-1.21-1.84SIbarite+1928.1SIbarite×T+aSr2+,aqaBa2+,aq-1Several theoretical models have also been compared against the experimental data. The birth and spread crystal growth model (B + S model) could accurately predict the solid composition of BaxSr1-xSO4 at higher barite SI and/or higher T conditions (barite SI = 1.5 at 70 °C and barite SI = 1.2–1.5 at 90 °C with [Sr2+]/[Ba2+] = 0.33–10). However, the B + S model predictions show larger deviations at lower SI and/or lower T conditions (barite SI = 0.9 and 1.2 at 50 °C and barite SI = 0.9 at 70 °C with [Sr2+]/[Ba2+] = 0.33–10 in this study). For other theoretical models, such as the CNT model and the BCF model, the predicted solid compositions of BaxSr1-xSO4 are significantly higher than the measured results. This quantitative study of the BaxSr1-xSO4 solid solution compositions could help reconstruct oceanic physical conditions and chemistry. It also establishes a solid foundation to further investigate the kinetics of the BaxSr1-xSO4 solid solution formation during non-equilibrium geological and industrial processes.

Remarkable fracture toughness of hypereutectic Nb-16Si-20Ti-2ZrC composites with fine primary γ-(Nb,X)5Si3 regulated by TiB2

To meet the requirements of the new generation of aeroengines, Nb-Si-based alloys have been widely studied as candidate materials for the new generation of blade materials; however, the lower ambient fracture toughness limits their applications. In this study, the effects of various contents (0, 0.5, 1, 3 at%) of TiB2 on the microstructure and ambient fracture toughness of the hypoeutectic composite of Nb-16Si-20Ti-2ZrC (base) composite were investigated. Ingots were manufactured via arc melting in an Ar atmosphere. Results demonstrate that the ingots were composed of Niobium based solid solution (Nbss) and γ-(Nb,X)5Si3, and TiC phases precipitate with a TiB2 content of 3 at%. A moderate amount of TiB2 (1 % TiB2 and below) markedly refined the microstructure, and the average phase sizes of Nbss and γ-(Nb,X)5Si3 decreased to 12.5 and 9.8 µm in the Nb-16Si-20Ti-2ZrC-1TiB2 composite, respectively. TiB2 promotes the movement of the eutectic point to the low Si side in the Nb-Si-based composite, transforming from a hypoeutectic (base) alloy to a eutectic alloy and a hypereutectic alloy. The ambient fracture toughness reached 18.6 MPa·m1/2, increased by 22 %. Many microcracks near the primary crack generated by the fine eutectic colony passivate the primary crack, and the deformation ability of the small-sized Nbss phase is enhanced, resulting in many dimples. The ambient fracture toughness of the Nb-16Si-20Ti-2ZrC-1TiB2 composite in this study is the highest among the reported as-cast Nb-Si-based composites, which can promote Nb-Si-based composites to meet the blade material requirements.

Structural investigation of ZrN+Si3N4 thin films co-deposited by magnetron sputtering

ABSTRACT Zirconium silicon nitride thin films with 1.6% Si addition were deposited via reactive magnetron sputtering and characterized by RBS, SEM-FEG, GAXRD, XPS and high temperature oxidation tests, aiming to investigate how silicon is structurally inserted in Zirconium nitride (ZrN) matrix. GAXRD results show a reduction in lattice parameter and grain size due to Si incorporation and XPS analyses demonstrate Si is present only in nitride form. Such observations proved the non-formation of substitutional or interstitial solid solution in ZrN, but the presence of Si3N4, even in low Si concentrations.

Effect of silicon on interfacial reaction and morphology of hot-dip aluminizing

Interfacial reaction and morphology are investigated between pure iron sheet and aluminum alloy with different silicon additions in hot-dip aluminizing (HDA) at 700 °C. The width of intermetallic reaction layer hot-dipped in a pure aluminum bath is mainly governed by the diffusion controlled growth of the η-Al5Fe2 phase. Al atoms can diffuse rapidly in a preferred [001] direction, resulting in the continuous growth of η phase with a tongue-like morphology. The addition of Si into aluminum baths reduces the growth rate of the reaction layer and eliminates the rough interface. The effect of Si inhibiting the growth of η phase can be attributed to the segregation of Si atoms at the Fe/Al interface and lead to the structural vacancy obstruction. The investigation reveals that the diffusion of Si at the interface will control the phase transformation of θ phase with a low Si content to higher Si containing τ1-Al2Fe3Si3 and τ5-Al8Fe2Si phase. The continuous τ1-Al2Fe3Si3 phase layer will be formed as the segregation concentration of the Si atoms reach 5 at.% at the interface between Al alloy and θ phase. And the continuous τ5-Al8Fe2Si layer is observed in the reaction layer of Al-6Si and Al-10Si, which will reduce the growth rate of η phase as a diffusion barrier.