Permeability of hydrogen in amorphous Pd(1−x)Six alloys at elevated temperatures

Hydrogen permeabilities of amorphous Pd_(1−x)Si_x (x=0.15, 0.175, 0.2) alloys in the form of ribbon, which were prepared with a single roller spinning technique, were measured at elevated temperatures up to 390°C. It was found that the hydrogen permeability of the amorphous alloys, strongly depending on the Si content, decreased with an increase in the Si content. The amorphous alloys possessed 3–5 times higher hydrogen permeability than the corresponding crystallized ones. The pressure dependence of hydrogen permeability in the amorphous alloys could be described by the simple n-th power equation, which was derived in this study.     

Anodic behavior of nickel-based alloys in the electrolytic production of NF3

The Ni-based alloys, such as Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si, prepared by hot isostatic pressing (HIP) at 1000 °C under 2 × 10⁸ Pa for 2 h were employed as the anodes for electrolytic production of NF₃. The current efficiencies for NF₃ formation were 42-38, 52-40, 52-47, 63-62, 50 and 41% for Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si alloys, respectively. The current efficiencies only on Ni-Cu alloys with Cu concentrations lower than 10 mol% were almost the same as those on Ni sheet and HIPed Ni anodes, whereas those on the other alloys used in this study were smaller compared with those on both Ni anodes. On the other hand, the current losses caused by anodic dissolution of Ni-Co, Ni-Mn, Ni-Ag, Ni-Cu, Ni-Al and Ni-Si alloy electrodes were 7.95-4.42, 6.40-7.02, 5.60-6.30, 3.34-6.33, 5.10 and 0.18%, respectively. The anode consumptions of Ni-5 mol% Cu and Ni-5 mol% Si alloys were almost the same or smaller compared with those of Ni sheet and HIPed Ni electrodes, though those of other alloys used were large compared with those of both Ni anodes. Consequently, addition of Cu to the nickel matrix is available for a cheaper cost of anode with keeping a same current efficiency as that on the Ni anode and addition of Si to the nickel matrix is effective for decreasing anode consumption largely. A Ni sheet electrode containing a trace of impurities, such as Co, Mn, Ag and Al, is also favorable as the anode for electrolytic production of NF₃.     

Solubility of hydrogen in amorphous Pd1−xSix alloys as hydrogen permeable membranes

Hydrogen solubility of amorphous Pd_1−xSi_x (x = 0.15, 0.175, 0.2) alloys in the form of ribbon, which were prepared with a single-roller melt spinning technique, was measured by a pressure-variable method at elevated temperatures up to 200°C. It was found that the hydrogen solubility in the amorphous alloys, strongly depending on the Si content, decreased with an increase in the Si content, and never obeyed the Sieverts law. The amorphous alloys showed 3–4 times higher hydrogen solubility than the corresponding crystallized ones. Based on the theory proposed by Kirchheim et al., an attempt was made to postulate a simplified equation to describe the relation between the pressure and composition of hydrogen in the amorphous alloys. As a result, similar to the half power law for the crystalline metal, the so-called nth power law with respect to pressure was found to be applicable for the amorphous Pd_1−xSi_x alloys.     

Frontispiece: Stainless Steel-Like Passivation Inspires Persistent Silicon Anodes for Lithium-Ion Batteries

Passivation of stainless steel by additives forming mass-transport blocking layers is widely practiced, where Cr element is added into bulk Fe−C forming the Cr₂O₃-rich protective layer. Here we extend the long-practiced passivation concept to Si anodes for lithium-ion batteries, incorporating the passivator of LiF/Li₂CO₃ into bulk Si. The passivation mechanism is studied by various ex situ characterizations, redox peak contour maps, thickness evolution tests, and finite element simulations. The results demonstrate that the passivation can enhance the (de)lithiation of Li-Si alloys, induce the formation of F-rich solid electrolyte interphase, stabilize the Si/LiF/Li₂CO₃ composite, and mitigate the volume change of Si anodes upon cycling. The 3D passivated Si anode can fully retain a high capacity of 3701 mAh g⁻¹ after 1500 cycles and tolerate high rates up to 50C. This work provides insight into how to construct durable Si anodes through effective passivation.     

Structure of amorphous hydrogenated silicon-nitrogen alloys studied by Fourier transform infrared spectroscopy

The structure of amorphous hydrogenated silicon-nitrogen alloys, potential materials for photovoltaic conversion and for micro-electronics, was studied in sight of their Fourier transform infrared spectra. The presence of NH vibration and the appearance of SiN stretching band with progressive decreasing of SiH₂ vibrational bands suggest that the incorporation of nitrogen is realized at the expense of SiH₂ groups leading to SiN bonds in structures of different local environments. A relationship has been established between the ν(SiH) frequency and the amount of nitrogen :

and offers an easy method for quantitative analyses.     

镁热还原气相法白炭黑制备纳米硅及其电化学性能

以气相法白炭黑(FS)为Si前驱体,通过镁热还原工艺和对获得的NPs-Si进行SiOx和C复合包覆,制备出NPs-Si@SiOx@C纳米复合结构,将其用作锂电池负极进行电化学性能测试。研究结果表明:镁热还原过程分两步进行,即SiO_2与Mg先生成Mg2Si中间相,Mg2Si继续与SiO_2反应生成Si的反应路径;根据此规律镁热还原气相法白炭黑的Si转化率达87.9%。电化学性能测试中NPs-Si@SiOx@C负极在2.0 A·g-1的电流密度下有1 300 mAh·g-1的容量平台,1 000次循环后的放电比容量为964.2mAh·g-1,容量保持率达75%。     

Thermodynamic Properties and Phase Equilibria in the Si-B System

Vapor composition and thermodynamic properties of silicon-boron alloys in the range of composition 1.5-100 at.% boron at 1522-1880 K were studied using Knudsen mass spectrometry. About 400 values of activities of both components at various compositions and/or temperatures were obtained. Liquid Si-B alloys were described as ideal associated solutions with the only associate B3Si. The phase diagram of the Si-B system was calculated on the basis of the obtained concentration and temperature dependences of thermodynamic functions for the formation of melts and intermetallic phases SiB₆ and SiB_n. The data obtained are in good agreement with previously published experimental data.     

Corrosion resistance of molybdenum silicides in aqueous solutions

The corrosion performance of Mo-22Si and Mo-25Si alloys in 0.5 M sodium chloride (NaCl) and 0.5 M sodium hydroxide (NaOH) solutions, at room temperature, was evaluated using electrochemical techniques. In 0.5 M NaCl, additionally, the effect of solution pH (3, 7 and 10) and concentration (0.1, 0.5 and 1.0 M) was studied using techniques such as potentiodynamic polarization curves, linear polarization resistance and electrochemical noise in current. The alloy contained either -Mo or Mo₅Si₃ phases in a Mo₃Si matrix. Polarization results showed that only the alloys containing 22Si developed a passive film in 0.5 M NaOH solution, whereas the alloy containing 25Si was passivated only in 0.5 M NaCl, pH 10 solution. In 0.5 M NaCl, pH 7 and 0.5 M NaOH solutions, the alloy with 25Si was the one with the highest corrosion rate, whereas the one containing 22Si was the most corrosion resistant. In NaCl solutions, the alloys exhibited a localized type of corrosion, but not in NaOH solutions. Alkaline NaCl solutions increased the corrosion rate of the 75Mo-25Si alloy with respect to acidic or neutral solutions, whereas diluted (0.1 M) or concentrated (1.0 M) NaCl solutions produced lower corrosion rates than the 0.5 M NaCl solution. Some localized type of corrosion occurred in the NaCl solutions, due to a selective corrosion of the -Mo and Mo₅Si₃ phases with respect to the Mo₃Si matrix.     

TEM and SNMS studies of protective alumina scales on NiCrAlY-alloys

The effect of Si addition on the oxidation behaviour of NiCrAlY alloys in the temperature range 950 bis 1100° C has been investigated. During isothermal oxidation oxide growth rates were practically independent of the Si-content. However during cyclic oxidation Si additions were beneficial. Si additions of 1–2^m/₀ appeared to shift the onset for spallation to longer times. It was found that Si stabilizes the -phase and probably it suppresses the formation of metastable Al₂O₃ modifications.     

Thermal plasma synthesis of transition metal nitrides and alloys

Applications of arc plasma processing to high-temperature chemistry of Group V nitrides and Si and Ge alloys are studied. The transition metal nitrides -VN, -NbN, and -TaN are directly synthesized in a dc argon-nitrogen plasma from powders of the metals. A large excess of N₂ is required to form stoichiometric -VN, while the Nb and Ta can only be synthesized with a substoichiometric N content. In a dc argon plasma the alloys V₃Si, VSi₂, NbSi₂, NbGe₂, Cr₃Si, and Mo₃Si are obtained from powder mixtures of the corresponding elements. The compounds are identified by x-ray diffraction patterns and particle shape and size are studied by electron microscopy.     

Interaction of Ca,P trace elements and Sr modification in AlSi5Cu1Mg alloys

Thermal and microscopy analyses were carried out to investigate the interaction of Sr modification with Ca and P trace elements in high-purity and commercial-purity Al–5Si–1Cu–Mg alloys. The results show how the addition of Sr to commercial-purity alloy induces significant changes in the nucleation and growth temperatures of eutectic Si since pre-eutectic Al₂Si₂(CaSr) intermetallics tend to poison AlP particles, making them inactive as nucleation sites for eutectic Si. In contrast, the addition of Sr to high-purity alloy shows no apparent influence on the characteristic temperatures of Al–Si eutectic reaction, even though the microstructural investigations reveal flake-to-fibrous transition in the eutectic Si structure. This indicates that the eutectic growth temperature, commonly used to predict eutectic modification level, is not a key feature of Sr modification, but it is indirectly caused due to the presence of additional impurities in commercial-purity alloys which affect the nucleation kinetics of eutectic Si.     

Microstructural and Mechanical Properties of Al-20%Si Containing Cerium

In this paper the effect of cerium addition in hypereutectic Al-Si alloys was studied. Casting method was used to produce Al-20Si with variation of Ce contents. The sample characterization studied was investigated by Optical Microscope, X-ray fluorescence and X-ray Diffraction. Vickers microhardness and wear test was carried out to study the influence of Ce towards the Al-20Si alloys. The addition of Ce in the Al-20Si alloys refined the Si primary phase as the Ce content increases. The results showed that the addition of 0.46 to 2.24 wt.% of cerium in Al-20Si alloys led to the formation of fine cells dispersed in the Al-matrix. These fine cells consist of a mixture of eutectic Si particles and intermetallic Al3Ce and CeAl1.2Si0.8 phase in Al matrix. The amount of rod- like intermetallic Al3Ce and CeAl1.2Si0.8 phase increases with increasing Ce content. The microhardness of Al-20Si alloys increases with the increase in Ce content. Addition of Ce up to 1.61 wt.% Ce improve the wear properties of Al-20Si alloy.     

Influence of the alloying effect on nickel K-shell fluorescence yield in Ni–Si alloys

Alloying effects on the K-shell fluorescence yield ω_K of nickel in Ni–Si binary alloy system have been studied by energy dispersive X-ray fluorescence. It is found that ω_K increases from pure Ni to Ni₂Si and then decreases from Ni₂Si to NiSi. These results are discussed in terms of d-occupation number on the Ni site and it is concluded that electronic configuration as a result of p-d hybridization explain qualitatively the observed variation of ω_K in Ni–Si alloys.     

On the System Silicon-Ytterbium: Constitution, Crystal Chemistry, and Physical Properties

Phase equilibria in the silicon-rich part of the system Si-Yb (>60 at.% Si) have been established from DTA, LOM, EMPA, and X-ray diffraction experiments on arc-melted and annealed bulk alloys as well as on single crystals grown from pure gallium or indium metal used as a flux solvent. Phase relations are characterized by the existence of a defect disilicide showing polymorphism. Yb₃Si₅, the low-temperature modification with Th₃Pd₅ type, is a line compound at 62.5 at.% Si, stable below 947±7°C. Above this temperature Yb₃Si₅ transforms into the YbSi_2−x (defect AlB₂-derivative type) corresponding to a peritectoid equilibrium at 947±7°C: YbSi_2−x+YbSi⇔Yb₃Si₅. YbSi_2−x exhibits a small homogeneity region from ∼62.5 at.% to ∼63.5 at.% Si and melts incongruently at 1408±9°C at ∼63 at.% Si. On cooling it decomposes according to a eutectoid reaction at 763±7°C: YbSi_2−x⇔Yb₃Si₅+(Si). The silicon-rich part of the diagram is characterized by a eutectic equilibrium at 1135+7°C and ∼81 at.% Si: L⇔YbSi_2−x+(Si). From magnetic susceptibility and electrical resistivity measurements, performed on single-crystalline specimens, Yb₃Si₅ was found to be an intermediate valent system.     

Reaction of silicon with alcohols in autoclave

A reaction of activated silicon with alcohols in an autoclave at 240—270 °C was studied. It was found that primary alcohols form tetraalkoxysilanes Si(OR)₄ with high selectivity (up to 97%), while the secondary PrⁱOH gave a mixture of compounds HSi(OPrⁱ)₃, Si(OPrⁱ)₄, HSi(OPrⁱ)₂OSi(OPrⁱ)₂H, HSi(OPrⁱ)₂OSi(OPrⁱ)₃, and Si(OPrⁱ)₃OSi(OPrⁱ)₃ with the predominance of trialkoxysilane (up to 67%). Carrying out the reaction under the indicated conditions has the advantage of experimental simplicity, reagent availability, high conversion of silicon, good isolated yields of products.     

A nuclear microprobe method for the simultaneous determination of silicon and nitrogen profiles in metals

A nuclear microprobe method has been developed for the simultaneous determination of silicon and nitrogen concentration profiles in metals. The method was based on the reactions²⁸Si(d, p₀)²⁹Si and¹⁴N(d, p₀)¹⁵N plus¹⁴N(d, β₀)¹²C with measurement of emitted charged particles during irradiation with 1.9 MeV deuterons. The nitrogen sensitivity was ten times that for silicon and the minimum concentrations detected were 0.002% and 0.03% respectively. The method was successfully applied to the measurement of silicon and nitrogen profiles in alloys contacted with silicon nitride at high temperature.     

Li15Al3Si6 (Li14.6Al3.4Si6), a compound displaying a heterographite‐like anionic framework

The title compound, lithium aluminium silicide (15/3/6), crystallizes in the hexagonal centrosymmetric space group P6₃/m. The three‐dimensional structure of this ternary compound may be depicted as two interpenetrating lattices, namely a graphite‐like Li₃Al₃Si₆ layer and a distorted diamond‐like lithium lattice. As is commonly found for LiAl alloys, the Li and Al atoms are found to share some crystallographic sites. The diamond‐like lattice is built up of Li cations, and the graphite‐like anionic layer is composed of Si, Al and Li atoms in which Si and Al are covalently bonded [Si—Al = 2.4672 (4) Å].     

Further studies on reactions of organic halides with disilanes catalysed by transition metal complexes

The interaction of a range of organic halides with (Cl₃Si)₂ or (Me₃Si)₂ in the presence of a variety of transition metal catalysts (very predominantly Pd⁰ or Pd^II complexes) have been examined. PhSiMe₃ was formed from PhCl[m.y., 15%] (m.y. - maximum yield), PhBr (m.y., 92%, with [PdL₂Br₂] as catalyst (L - PPh₃)), and (contrary to earlier reports) PhI (m.y. 51%, with [PdL₂I₂]). MeSiCl₃ was formed from MeBr (m.y., 78% with [PdL₄]) and MeI (m.y., 91% with [PdL₄]), and EtSiCl₃ from EtBr (m.y., 49%, with [PdL₂“Br₂]; L” - P(C₆H₄OMe-p)₃) and EtI (m.y. 45%, with [PdL₄]). Me₄Si was satisfactorily formed from MeBr (m.y. 42%, with [PdL₄]). Evidence was obtained for the formation of Me₃SiCF₃ from CF₃I. Very poor yields of XC₆H₄CH₂SiMe₃ were obtained from XC₆H₄CH2Br (X - H orp-Me) (with X - H some PhSiMe₃ was formed), butp-O₂NC₆H₄CH₂SiMe₃ was formed in 48% yield fromp-O₂NC₆H₄CH₂Cl with [PdL“₄] as catalyst. PhCOSiMe₃ was formed from PhCOCl (m.y. 52% with [PdL₂I₂]. The nickel complex [NiL₄] was moderately effective as a catalyst for reactions between (Cl₃Si)₂ and MeBr, EtBr, or PhCH₂Br. The new complex [PdL₂(SiCl₃)₂] was prepared by treatment of [PdL₄] with (Cl₃Si)₂ or Cl₃SiH, and shown to catalyse the reaction between MeBr and (Cl₃Si)₂.     

Effect of charge on bond strength in hydrogenated amorphous silicon

We have studied the effect of excess charge on the bond strength in the silanes SiH₄ and Si₂H₆ to assess whether charge trapping in a solid-state lattice might promote the technologically important photodegradation of amorphous silicon alloys (the Staebler-Wronski effect). The calculations indicate that both positive and negative charges reduce the strength of Si? H and Si? Si bonds considerably, to the point where they may be broken easily by visible or even infrared light. © 1994 by John Wiley & Sons, Inc.     

Non-hydrolytic synthesis of titanosilicate xerogels by acetamide elimination and their use as epoxidation catalysts

Novel non-hydrolytic syntheses of titanosilicate xerogels by polycondensation of silicon acetate, Si(OAc)₄, with titanium (IV) dimethylamide or diethylamide, Ti(NR₂)₄ (R?=?Me, Et), are presented. The reactions are based on acetamide elimination and yield gels with a high content of Si?CO?Ti bonds in comparison with the ester elimination route. Although a ligand exchange was observed, it was interestingly not followed by homo-condensation and during the synthesis the phase separation to SiO₂ and TiO₂ was avoided. The degree of condensation reached up to 68?%. The xerogels prepared for a comparison by ester elimination from Si(OAc)₄ and titanium (IV) isopropoxide featured a significantly lower content of the Si?CO?CTi bonds. The initial tests in the epoxidation of cyclohexene by cumyl hydroperoxide (CHP) indicated a high selectivity and moderate activity of the xerogels. The catalytic properties were significantly improved by combining non-hydrolytic and hydrolytic methods yielding mesoporous and homogeneous Si/Ti mixed oxides. The catalysts prepared by these methods provided a complete epoxidation of cyclohexene in 2?h at?65?°C.