Reaction Of Si Research Articles

Burning and radiance properties of Si in AP/HTPB based compositions

Silicon (Si) has high caloric power and its combustion product silica (SiO2) shows high emissivity in the far infrared (8–14 μm). The study adds different contents of Si into the Ammonium Perchlorate/Hydroxyl-terminated polybutadiene (AP/HTPB) based compositions, aiming to investigare the influence of Si on the burning and radiance properties of AP/HTPB based compositions by using a FTIR remote-sensing spectrometer, a Fourier Transform Infrared Spectrometer, a far-infrared thermal imager and a synchronous thermal analysis instrument. The experimental results show that the combustion oxidation reaction of Si is restricted by the oxygen balance of the system. When the oxygen balance exceeds 25 (Si content is greater than 15%), the insufficient oxygen supply makes the combustion rate significantly reduced from 0.52 g/s to 0.36 g/s, and Si cannot be closely related to the infrared performance and combustion of the AP/HTPB agent. When the Si content is less than 15%, the infrared radiation energy of the entire infrared band of AP/HTPB can be increased, and as the Si content increases, the radiation temperature increases rapidly from 342 °C to 1070 °C, and the far-infrared radiation intensity increases from 1.56 W/Sr to 7.81 W/Sr. The smallest mid-to-far infrared radiation ratio of 3 can be obtained when the Si content is 15%. Therefore, Si has a positive effect on improving the infrared radiation performance of AP/HTPB.

Precise resonance energies measured for energy calibration of particle accelerator using thin silicon–nitride foils

In this work resonance parameters of the 28Si(p,p′γ)28Si (Eγ = 1779 keV) and 14N(p,p′γ)14N (Eγ = 2313 keV) reactions were measured between 3 and 4 MeV proton energies for absolute proton beam energy calibration of particle accelerators. For the measurements commercially available self-supporting thin silicon–nitride films and a HPGe gamma-detector were used which are readily available in most accelerator laboratories. Based on our measurement and on the assessment of literature data, the following resonance energies and widths are recommended: 3100.6 ± 0.9 keV (Γ = 11.9 ± 0.4 keV) and 3338.1 ± 1.0 keV (Γ = 11.0 ± 0.5 keV) in 28Si(p,p′γ)28Si and 3903.1 ± 1.7 keV (Γ = 98 ± 1 keV) and 3991.6 ± 1.1 keV (Γ = 10.8 ± 0.5 keV) in 14N(p,p′γ)14N. In addition to the resonance measurements, absolute thick target yields and gamma-ray angular distributions were measured for the 28Si(p,p′γ)28Si (Eγ = 1779 keV) reaction in the vicinity of Ep = 3.10 and 3.34 MeV for ion beam analysis purposes using a thick silicon wafer target.

Status of the Mg24(α,γ)Si28 reaction rate at stellar temperatures

The $^{24}$Mg($\alpha,\gamma$)$^{28}$Si reaction influences the production of magnesium and silicon isotopes during carbon burning and is one of eight reaction rates found to significantly impact the shape of calculated X-ray burst light curves. The reaction rate is based on measured resonance strengths and known properties of levels in $^{28}$Si. The $^{24}$Mg($\alpha,\gamma$)$^{28}$Si reaction rate has been re-evaluated including recent additional indirect data. The reaction rate is substantially unchanged from previously calculated rates, especially at astrophysically important temperatures. Increases in the reaction rate could occur at lower temperatures due to as-yet unmeasured resonances but these increases have little astrophysical impact. The $^{24}$Mg($\alpha,\gamma$)$^{28}$Si reaction rate at temperatures relevant to carbon burning and Type I X-ray bursts is well constrained by the available experimental data. This removes one reaction from the list of eight previously found to be important for X-ray burst light curve model-observation comparisons.

Study on γ-ray source from the resonant reaction 19F(p,αγ) 16O at E p = 340 keV*

High energy γ-ray can be used in many fields, such as nuclear resonant fluorescence, nuclear medicine imaging. One of the methods to generate high-energy γ-ray is nuclear resonant reaction. The 19F (p,αγ) 16O reaction was used to generate 6.13-MeV γ-ray in this work. The angular distribution of 6.13-MeV γ-ray was measured by six LaBr3 detectors. The thick-target yield curve of 6.13-MeV γ-ray had been measured. The maximum yield was determined to be (1.85 ± 0.01) × 10−8 γ/proton, which was measured by HPGe detector and LaBr3 detector. The absolute efficiency of all the detectors was calibrated using 60 Co and 27Al (p,γ) 28Si reaction at E p = 992 keV. The cross section and total resonant width of the reaction were determined to be 95.1±1.0 mb (1 b = 10−24 cm2) and Γ CM = 2.21±0.22 keV, respectively.

Potential Dependence of Electrochemical Etching Reaction of Si(111) Surface in a Fluoride Solution Studied by Electrochemical and Scanning Tunneling Microscopic Techniques

Potential Dependence of Electrochemical Etching Reaction of Si(111) Surface in a Fluoride Solution Studied by Electrochemical and Scanning Tunneling Microscopic Techniques

Exploring neutron capture therapy with 33S and 10B

The 33S(n,α)30Si reaction was proposed as cooperative neutron capturer to 10B(n,α)7Li in Neutron Capture Therapy (NCT). At that moment, the available 33S(n,α)30Si cross-section data were scarce and discrepant in key energy ranges for its use in NCT. Since then, three experiments have been carried out at n_TOF facility at CERN and at Institut Laue-Langevin. These new data are used for the calculation of the dose rate on ICRU-4 tissue by using kerma factors, a simplified model of tissue and a 13.45 keV neutron beam, energy of the most important 33S(n,α)30Si resonance. A significant enhancement of the dose rate due to the presence of 33S is shown. In spite of the limitations, the cooperative action of 33S and 10B is an interesting possibility to be studied for accelerator-based neutron sources with non-moderated neutrons.

Synthesis mechanism of amorphous Si2BC3N powders: Structural evolution of 2Si‐BN‐3C mixtures during mechanical alloying

AbstractA detailed knowledge of structural evolution during mechanical alloying (MA) is of interest and critical for understanding of synthesis mechanism, optimization of milling process, and control of milling products. The structural evolution of the 2Si‐BN‐3C mixture with a molar ratio of Si:BN:C = 2:1:3 during MA was studied by investigating the changes of phases, morphologies, elemental distributions, microstructures, and chemical bond states using XRD, SEM‐EDS, TEM, XPS, and Raman. With the increases in milling time, the particle sizes of the milled 2Si‐BN‐3C powders first decrease to submicrometers (~1 hour), slightly increase afterward (~3 hours), and eventually decrease to nanoscales gradually reaching equilibrium (≥10 hours). Depending on the intrinsic crystal structures of themselves, h‐BN and graphite are almost amorphized after milling of 10 hours, while amorphization of c‐Si takes at least 20 hours. The same milling parameters can provide amorphous Si2BC3N powders, but incompletely amorphous (partially crystalline) SiC powders, which is mainly due to the dilution effect of B and N atoms on the atomic concentration of Si and C hindering the microdiffusion and subsequent mechanochemical reaction of Si and C. Crystallite refinement–induced amorphization is the major synthesis mechanism of amorphous Si2BC3N powders. This work would offer more insight into the MA synthesis of multiple component materials, especially Si‐based brittle systems.

Synthesis and Electrochemical Performance of π-Conjugated Molecule Bridged Silicon Quantum Dot Cluster as Anode Material for Lithium-Ion Batteries.

π-Conjugated molecule bridged silicon quantum dots (Si QDs) cluster was prepared by Sonogashira C–C cross-coupling reaction between 4-bromostyryl and octyl co-capped Si QDs (4-Bs/Oct Si QDs) and 1,4-diethynylbenzene. The surface chemical structure, morphology, and chemical composition of the Si QD cluster were confirmed by Fourier transform infrared spectroscopy, field emission transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Lithium-ion batteries were fabricated using 4-Bs/Oct Si QD and Si QD clusters as anode materials to investigate the effect of QD clustering on the electrochemical performance. Compared with the 4-Bs/Oct Si QD electrode, the Si QD cluster exhibits improved electrochemical performance, such as a high initial discharge capacity of ∼1957 mAh/g and good cycling stability with ∼63% capacity retention following 100 cycles at a current rate of 200 mA/g when tested at the voltage window of 0.01–2.5 V. The improved electrochemical performance of the Si QD cluster is attributed to the π-conjugated molecules between the Si QDs and on the surface of Si QD cluster, which serve as a buffer layer to alleviate the mechanical stresses arising from the alloying reaction of Si with lithium and maintain the electrical conduits in the anode system.

Study of the Mechanism of the 27Al(α, p)30Si Reaction at Eα = 30.3 MeV

The results from measuring the angular dependence of the 27Al(α, p)30Si reaction differential cross sections at 30.3 MeV α-particle energy with the formation of the final nucleus in the ground (0+) and first excited (2+; 2.235 MeV) states are presented. The experimental results are compared to calculated ones obtained by assuming there is both a mechanism of triton cluster stripping in a collective model and one of compound nucleus formation. The amplitudes of spectroscopic factors for the virtual decay of 30Si → 27Al + t are obtained using a shell model with wave functions of the 1d–2s shell nuclei in the Nilsson model, allowing for nuclear deformation and the spin–orbit interaction of nucleons. Comparison of the results from calculations and experiments shows that mechanism of triton stripping used in the FRESCO code with the obtained spectroscopic amplitudes mainly describes both the shape of angular distributions and the absolute values of the differential cross sections. The contribution from the mechanism of compound nucleus formation is notable only at large angles of proton emission.

Interplay between solution chemistry and mechanical activation in friction-induced material removal of silicon surface in aqueous solution

Shear-induced chemical etching reactions of single-crystalline Si(100), Si(110), and Si(111) surfaces were studied in acidic, neutral, and basic aqueous solutions. Measuring the applied load dependence of substrate etching yield and analyzing the data with the mechanically-assisted thermal activation model, the critical activation volume and activation barrier were determined for mechanochemical etching of three crystallographic surfaces. The pH dependence of Si(110) etching is quite distinct from those of Si(100) and Si(111). The results suggested that the mechanochemical activation effect is larger for Si(100) and Si(111) than Si(110) which is chemically more reactive than the other two surfaces. The findings of this study may provide deeper insights for mechanistic understanding of the scanning probe microscopy based nanomanufacturing and chemical mechanical polishing processes.

Ge/SiGe multiple quantum well fabrication by reduced-pressure chemical vapor deposition

In this paper we deposit structures comprising a stack of 10 periods made of 15-nm-thick Ge multiple quantum wells (MQWs) enclosed in a 15-nm-thick Si0.2Ge0.8 barrier on SiGe virtual substrates (VSs) featuring different Ge content in the 85%–100% range to investigate the influence of heteroepitaxial strain on Si0.2Ge0.8 and Ge growth. With increasing Ge concentration of the VS, the growth rate of Si0.2Ge0.8 in the MQWs increases. Si incorporation into the Si0.2Ge0.8 layer also becomes slightly higher. However, almost no influence of the growth rate is observed for Ge growth in the MQWs. We argue that increased tensile strain promotes the Si reaction at the surface. In the case of Si0.2Ge0.8 growth on Ge, we observe a smeared interface due to Ge segregation during the growth. Furthermore, we observe that the interface width increases with increasing Ge concentration of the VS. We attribute this observation to the increased segregation of Ge driven by increased strain energy accumulated in the Si0.2Ge0.8 layers. We also observe that the MQW layer “filters out” threading dislocations formed in the VS.

Simultaneous measurement of β -delayed proton and γ emission of P26 for the Al25(p,γ)Si26 reaction rate

$\beta$ decay of $^{26}$P was used to populate the astrophysically important $E_x=$5929.4(8) keV $J^{\pi}=3{^+}$ state of $^{26}$Si. Both $\beta$-delayed proton at 418(8) keV and gamma ray at 1742(2) keV emitted from this state were measured simultaneously for the first time with corresponding absolute intensities of 11.1(12)\% and 0.59(44)\%, respectively. Besides, shell model calculations with weakly bound effects were performed to investigate the decay properties of other resonant states and a spin-parity of $4^+$ rather than $0^+$ was favored for the $E_x=$5945.9(40) keV state. Combining the experimental results and theoretical calculations, $^{25}$Al($p,\gamma$)$^{26}$Si reaction rate in explosive hydrogen burning environments was calculated and compared with previous studies.

Mechanically activated SHS of Nb5Si3 and Nb5Si3/Nb composites

Nb5Si3 and Nb are the main components of niobium silicide-based composites, which are promising materials for high-temperature structural applications. Self-propagating high-temperature synthesis (SHS) is an attractive method for fabricating advanced materials from powders via exothermic reactions between the mixture constituents. However, to overcome kinetic difficulties of Nb–Si reaction, SHS of niobium silicides usually requires additional heat input. The present work focuses on a technique that addresses this problem by adding a mechanical activation step before SHS. Specifically, short-term ball milling was used for mechanical activation of Nb/Si mixtures with the goal of conducting SHS of Nb5Si3 and Nb5Si3/Nb composites with no preheating. The milled mixtures were compacted and ignited in an argon environment. It has been shown that a planetary mill is an effective tool for mechanical activation of Nb/Si mixtures. Milling for 10 min enabled SHS of the product that consisted of α-Nb5Si3 and γ-Nb5Si3 phases with traces of Nb3Si. For the first time, Nb5Si3/Nb composites were obtained by mechanically activated SHS with no preheating. Combustion took place at an Nb/Si mole ratio as high as 3, i.e. at 25 at% Si in the mixture. At this mole ratio, a spinning propagation of the combustion wave was observed, and the content of the γ phase, which has poor mechanical properties, was dramatically decreased.

Enhancing the electrochemical properties of a Si anode by introducing cobalt metal as a conductive buffer for lithium-ion batteries

Silicon anodes have attracted extensive attention due to their high theoretical capacities (3579 mAh g−1) and low working potential (<0.5 V). However, Si suffers from low electrical conductivity (6.7 × 10−4 S cm−1) and pulverization of silicon particles during charging/discharging. To prevent the degradation of Si anodes, many approaches, such as introducing a mechanical buffer, have been conducted to reduce the mechanical stress on Si. Among these approaches, introducing electrically conductive materials is desirable in that it can also reduce the internal resistance of the Si electrode. In this work, we synthesized a Si/SiOx/Co composite using a conversion reaction of CoO and Si at 900 °C under continuous nitrogen flow. Co metal with face-centered cubic (fcc) structure in the Si/SiOx/Co composite can act as a mechanical buffer as well as a conductive agent due to its high ductility. As a result, the Si/SiOx/Co anode exhibited a high specific capacity of 1602 mAh g−1Si/SiOx after 200 cycles at a current of 2 A g−1. The Si/SiOx/Co composite is suitable for lithium-ion batteries (LIBs) due to its facile synthetic method and high electrochemical performance.

Preparation and microstructure characterization of SiC/SiC joints reinforced by in-situ SiC nanowires

A novel two-step joining technology (pyrolysis and C–Si reaction bonding) to prepare in-situ SiC nanowires reinforced SiC/SiC joints were developed. The multi-component slurry consisting of polycarbosilane (PCS, preceramic polymer) and ferrocene (catalyst) were designed and optimized to join the sintered SiC ceramics. Microstructure of the joining layer after pyrolysis and joints after C–Si reaction bonding were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In addition, PCS-derived products and growth mechanism of SiC nanowires inside the joining layer were discussed. The results showed that 4 wt% castor oil and 3 wt% phenolic resin were proven to be the optimized dispersant content and binder content of the slurry to obtain the top-quality joining layer. With the increase of PCS content in the slurry, the generated SiC nanowires inside the joining layer became straight and diameter increased. After C–Si reaction bonding, the SiC nanowires were retained and distributed randomly in the joining layer. PCS-derived products after pyrolysis consisted of β-SiC and free carbon, and later gradually increased with rise of pyrolysis temperature. The SiC nanowires inside the joining layer grew up following the Vapor-Liquid-Solid (VLS) mechanism and gaseous substances used for the growth were mainly comprised of CH4, SiH4 and CH3SiH3.

Study of the {{^{25}}}Mg(d,p){{^{26}}}Mg reaction to constrain the {{^{25}}}Al(p,{gamma }){{^{26}}}Si resonant reaction rates in nova burning conditions

The rate of the ^{25}Al(p, gamma )^{26}Si reaction is one of the few key remaining nuclear uncertainties required for predicting the production of the cosmic gamma -ray emitter ^{26}Al in explosive burning in novae. This reaction rate is dominated by three key resonances (J^{pi }=0^{+}, 1^{+} and 3^{+}) in ^{26}Si. Only the 3^{+} resonance strength has been directly constrained by experiment. A high resolution measurement of the ^{25}Mg(d, p) reaction was used to determine spectroscopic factors for analog states in the mirror nucleus, ^{26}Mg. A first spectroscopic factor value is reported for the 0^{+} state at 6.256 MeV, and a strict upper limit is set on the value for the 1^{+} state at 5.691 MeV, that is incompatible with an earlier (^{4}He, ^{3}He) study. These results are used to estimate proton partial widths, and resonance strengths of analog states in ^{26}Si contributing to the ^{25}Al(p, gamma )^{26}Si reaction rate in nova burning conditions.

In situ synthesis of MOF-derived carbon shells for silicon anode with improved lithium-ion storage

Silicon (Si) has been broadly investigated as a promising anode in lithium-ion batteries (LIBs). However, there is still a problem that the alloying reactions of Si and Li often cause structural failures and rapid degradation in capacity of the electrode. Herein, an in-situ encapsulation of Si nanoparticles forming metal-organic-framework (MOF) derived carbon shells has been developed to improve the performance and retain the structural integrity of the electrode. Using this strategy, a compact and robust interface was ensured between the Si nanoparticles and carbon shell while also reducing the unnecessary exposing areas simultaneously. Moreover, the pores in the MOF-derived carbon shells offered good channels for Li-ion penetration and diffusion. The resulted composite electrode exhibited excellent electrochemical performance and delivered a capacity of 3714 mAh g−1 at 200 mA g−1, and an outstanding reversible capacity of 820 mAh g−1 at 5000 mA g−1 even after 1000 cycles, Direct comparison between the encapsulated Si and naked Si revealed the significance of the MOF-derived carbon shells and its great potential for the next-generation high capacity LIBs.

Si and Ge-Based Anode Materials for Li-, Na-, and K-Ion Batteries: A Perspective from Structure to Electrochemical Mechanism.

Silicon and germanium are among the most promising candidates as anodes for Li-ion batteries, meanwhile their potential application in sodium- and potassium-ion batteries is emerging. The access of their entire potential requires a comprehensive understanding of their electrochemical mechanism. This Review highlights the processes taking place during the alloying reaction of Si and Ge with the alkali ions. Several associated challenges, including the volumetric expansion, particle pulverization, and uncontrolled formation of solid electrolyte interphase layer must be surmounted and different strategies, such as nanostructures and electrode formulation, have been implemented. Additionally, a new approach based on the use of layered Si and Ge-based Zintl phases is presented. The versatility of this new family permits the tuning of their physical and chemical properties for specific applications. For batteries in particular, the layered structure buffers the volume expansion and exhibits an enhanced electronic conductivity, allowing high power applications.

Measurements of the 33S (n, α)30Si cross-section at n_TOF and ILL: Implications in neutron capture therapy

Up to a couple of years ago, the 33S(n, α)30Si cross-section data had been limited and scarce. The origin in the solar system of 36S had been the only motivation to study that cross-section. However, a few years ago, the 33S(n, α)30Si reaction was proposed as a possible target in neutron capture therapy (NCT) due to the excellent bio-properties of 33S and the significant resonance at 13.45 keV of the cross-section for which a high-energy α is emitted. Prior to the experiments carried out at n_TOF-CERN and at the Institut Laue-Langevin (ILL) facilities, the data situation was: no data from the thermal point up to 10 keV; from 10 keV to 300 keV, there was only one (n, α) measurement able to resolve the resonances with a questionable value of the 13.45-keV resonance; and the thermal point did not have a consistent value. Here we summarize three experiments that have been performed covering the whole energy range of interest in NCT and astrophysics. These experiments have solved the most important issues. The data of the present work and the evaluated data are used to calculate the dose rate in the tissue.

Analysis of Ancient Glass Using Ion Beams and Related Techniques

Ion Beam Analysis (IBA) techniques are established as an indispensable tool for material analysis. They are very powerful when applied to the examination of uniform layers. In recent years they have been also used for the quality control of implanted layers, which improve the mechanical or chemical properties of common materials. The use of IBA techniques for the study of corrosion is impeded by the non-uniformity of such layers, which renders the analysis difficult. In the Material Analysis Laboratory of the Institute of Nuclear Physics, a combination of experimental techniques and analytical algorithms has been developed, which allows the non-destructive examination of corrosion layers on cultural artifacts. Ancient glass fragments from Kenchreai, Greece, were analyzed with ion beam techniques, in order to examine the applicability of the latter to the characterization of the surface. The relative distribution of heavy components was determined by X-Ray Fluorescence (XRF). Nuclear reactions were used to determine the depth distribution of H, O, C and Si. The Hydrogen distribution rises sharply from the surface, reaching a maximum of 9xl022 at/cm3 at 0.5 μπι and then decays smoothly to a depth of approximately 2 μπα. Examination of the same samples with aparticles, indicates a depletion of Silicon in the same surface region, while the Oxygen distribution is uniform. A detailed analysis, using the 28Si(p, p) reaction, which resonates at 2.095 MeV, confirms the depletion and other non-uniformities in the Silicon distribution.