Addition Of Bi Research Articles

Effect of Bi Content on the Microstructure and Mechanical Performance of Sn-1Ag-0.5Cu Solder Alloy

The purpose of this work is to explore the impact of 0.5, 1.5, 2.5 and 3.5 wt.% Bi additions on the microstructure and mechanical performance of Sn-1Ag-0.5Cu solder alloy. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were utilized to examine the microstructure of the present solders. Creep measurements have been used for the preliminary assessment of mechanical properties. The steady-state creep rate, έst, diminished as the Bi’s concentration increased and reached 2.5 wt.%, with this trend altering above this point. Furthermore, increasing the aging or testing temperature caused the έst values to increment for all the investigated solders. έst variations with different Bi content and aging temperature were observed by examining the Sn-Ag-Cu solders’ structural evolutions. The mean value of the activation energy of all investigated solder alloys was found to be ∼52 kJ/mol. This value is appropriate to that quoted for the dislocation climb through the core diffusion as the dominant operating mechanism. The XRD findings supported the microstructure and lattice parameters variations with both aging temperatures and bismuth concentrations.

The influence of Ga, Sn, or Bi addition on the electrochemical behavior and discharge performance of Al–Zn–In anodes for Al-air batteries

In this work, experimental methods, such as electrochemical measurements, hydrogen collection technique, battery performance tests, and microstructure analysis, are used to investigate the electrochemical properties and discharge behaviors of Al–4.5Zn–0.05In and Al–4.5Zn–0.05In–0.05Ga/Sn/Bi anodes in 4 M NaOH solutions. Results suggest that the discharge performance of Al–Zn–In anodes can be further enhanced by adding Ga, Sn, or Bi elements. These elements show a dissolution-deposition behavior on the anode surface, which reduces the resistance of the passive film and increases the activity of active sites on the electrode surface. Also, adding Sn or Bi works better than adding Ga. Because Ga element is likely to cause severe local corrosion at the grain boundaries. Furthermore, the peak energy densities of Al–4.5Zn–0.05In–0.05Sn and Al–4.5Zn–0.05In–0.05Bi anodes at 40 mA cm−2 are approximately 3628.64 Wh kg−1 and 3456.12 Wh kg−1, respectively, which are 29.6% and 23.5% higher than that of Al–4.5Zn–0.05In anodes.

Sn and Bi whisker growth from SAC0307-Mn07 and SAC0307-Bi1-Mn07 ultra-thin film layers

In the past years, the use of low silver content SAC0307 (99Sn0.3Ag0.7Cu wt%) solder alloy grew considerably due to its good soldering quality. In the latest version of this alloy, manganese, and bismuth are used to improve further its soldering parameters. In this study, a reliability issue, the whisker growth from SAC0307-Mn07 and SAC0307-Bi1-Mn07 solder alloys was investigated. Ultra-thin films (in 100–150 nm thickness) were vacuum evaporated from the investigated alloys onto Cu substrates. The samples were stored at laboratory conditions for 28 days. Whisker growth was followed by a scanning electron microscope, and the ultra-thin film layers structures were investigated in focused ion beam cuts. In the case of the SAC0307-Mn07, the mechanical stress due to the intermetallic layer growth resulted in whisker formation right after the layer deposition. However, Bi addition could increase the stress relaxation ability of the ultra-thin film layer; the whisker formation started only three days after the evaporation in the case of the SAC0307-Bi1-Mn07 layer. Besides, the SAC0307-Bi1-Mn07 alloy could entirely suppress the formation of filament-type whiskers that might cause reliability issues in microelectronics. Furthermore, a unique phenomenon was observed that the SAC0307-Bi1-Mn07 layer produced mostly Bi–Sn whisker couples.

Influence of Bi2O3 co-doping on Cr-doped ZnGa2O4 red persistent phosphors synthesized by a liquid phase precursor process

The long persistence luminescent property of Cr-doped ZnG2O4 phosphor in the deep red/near-infrared region has been of great interest for the purpose of in vivo bioimaging application. Improving the optical property and afterglow lifetime of this material remain challenging. The microcrystalline cellulose assisted liquid phase precursor process was developed for the synthesis of high-quality ZnGa2O4 phosphors, which process enables uniform distribution of the dopant and co-dopant. In this paper, the co-doping of Bi enhanced the photoluminescence intensity by about 2.5 times, while significantly improving the long afterglow property. Investigation of the influence of the Bi addition indicated that the co-doping Bi not only serves to purify Cr ions in ZnGa2O4, but also brings about the growth of particles and changes in morphology through the role of flux.

Effects of bismuth additions on mechanical property and microstructure of SAC-Bi solder joint under current stressing

Bi additions have been reported to improve the wettability and drop-impact performance. Most important of all, it improves the mechanical properties. However, few studies focus on the effect of the Bi addition on mechanical properties and microstructure of intermetallic compounds (IMCs) in solder balls, especially on those properties after current stressing. In this study, to understand the effect of Bi addition, a lead-free Sn-3Ag-0.5Cu-xBi (SAC305-Bi) solder joint with Bi additions from 1 to 3 wt% was used to investigate mechanical property of Sn-rich matrix and microstructure of IMCs in the solder joint after current stressing process. We combined nanoindentation, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) to analyze mechanical property, and observe the intermetallic compounds of Cu3Sn, and Cu6Sn5 at the interface. The mechanical properties of hardness in Sn matrix is improved by the amount of Bi, where the hardness increases from 0.095 to 0.141 GPa as increasing Bi addition from 1 to 3 wt%. In addition, the growth rate constant of intermetallic compounds of Cu3Sn is in the range between 0.175 and 0.256, that is, Cu3Sn is not sensitive to Bi addition. Furthermore, the amount of doping Bi addition enhances the growth rate Cu6Sn5, as the rate constant increases from 1.597 to 2.413 with increasing Bi addition from 1 to 3 wt%.

Synthesis, structural refinement and physical properties of novel perovskite ceramics Ba1-xBixTi1-xMnxO3 (x = 0.3 and 0.4)

The crystal structure, morphological, optical, electrical and dielectric properties of polycrystalline perovskites of Ba1-xBixTi1-xMnxO3 (x = 0.3 and x = 0.4), prepared by the standard solid-state reaction process, were investigated systematically. From the X-ray diffraction results at ambient temperature, both samples showed the pure perovskite phase. Rietveld refinements revealed that the studied compounds adopt the cubic structure symmetry with Pm3‾m as a space group. Scanning electron microscopy demonstrated that the samples show irregularly spherical grains with an average size of 2 μm. From UV–vis–NIR absorption spectra, the synthesized compounds exhibit a maximum absorbance in the whole visible range. Furthermore, the direct band gap energy was found to be 1.07 and 0.85 eV for x = 0.3 and 0.4, respectively. The electrical transport in these materials was studied by using the impedance spectroscopy from the room temperature to 110 °C. The modelling of complex impedance data was performed to separate the grain and grain-boundary contributions in the conduction process. The addition of Bi and Mn ions increased the dc electrical conductivity. The thermal variation of the dc electrical conductivity proved the semiconductor behavior of both studied compounds. The obtained activation energies from the dc conductivity for grain and grain-boundary contributions were found to be 0.39–0.36 eV for x = 0.3 and 0.20–0.32 eV for x = 0.4. The conduction mechanism was explained by hopping process along ionized oxygen vacancies. The dielectric permittivity and dielectric loss of both compositions showed an increase with increasing temperature.

Effect of Bi addition on the shear strength and failure mechanism of low-Ag lead-free solder joints

To optimize the mechanical properties of low-Ag lead-free solder, different amount of Bi element was added into the Sn–1.0Ag–0.5Cu (SAC105) to form SAC105-xBi (0 ≤ x ≤ 4) solder alloy. The microstructural evolution and shear fracture of SAC105-xBi solder joints were systematically investigated to clarify the failure mechanism after reflow and after 175 °C aging compared to SAC305. It was found that Bi element could provide solution strengthening and second-phase strengthening in the low-Ag SAC solder joints depending on the amount of added Bi element. The shear strength after reflow increased from 34.79 to 70.16 MPa with the increase of Bi addition from x = 0.0 to x = 4.0, while that after aging at 175 °C for 168 h increased from 28.97 MPa (x = 0.0) to 55.02 MPa (x = 4.0). The thickness of IMC decreased with the addition of Bi, and excessive Bi would precipitate in the matrix when the Bi content reached 2 wt% or even form brittle Bi barrier layer after 4 wt% addition. During shear tests, three kinds of fracture mode including ductile fracture, quasi-cleavage fracture, and cleavage brittle fracture were observed, and three kinds of failure position including solder matrix, Cu6Sn5/solder interface, and Cu3Sn/Cu interface were revealed. The failure mechanism of different solder joints was closely related to the coupling effects among the Bi amount in the matrix, the thicknesses of IMC, and the status of Kirkendall voids, which significantly affected the reliability of SAC solder joints. Finally, SAC105-1.0Bi solder alloy was considered having the most suitable Bi addition with anticipated comprehensive properties compared with SAC305.

Pengaruh Agen Kimia Berbeza terhadap Penguraian Terma dan Pembentukan Fasa Bahan La0.6SR0.4CoO3- δ yang Disediakan melalui Kaedah Sol-Gel

Sifat penguraian terma dan pembentukan fasa bahan lantanum strontium kobalt oksida, La0.6Sr0.4CoO3-δ (LSC) yang disediakan melalui kaedah sol-gel berbantu agen kimia berbeza, iaitu agen serakan, agen pempolimeran dan agen permukaan aktif atau surfaktan telah dicirikan secara sistematik masing-masing melalui analisis termogravimetrik (TG) dan pembelauan sinar-X (XRD). Penguraian terma bahan organik dan bahan bukan organik yang tidak diperlukan dalam serbuk pelopor bahan LSC telah lengkap pada suhu kurang daripada 1000 °C bagi serbuk pelopor yang disediakan dengan menggunakan agen serakan dan agen pempolimeran, dan suhu melebihi 1000 °C bagi serbuk pelopor yang disediakan dengan menggunakan surfaktan. Sifat penguraian terma ini dipengaruhi oleh suhu pengeringan serbuk pelopor tersebut dan berat molekul agen kimia. Pembentukan fasa tunggal perovskit LSC telah disahkan dalam serbuk pelopor yang disediakan dengan menggunakan agen serakan, iaitu karbon teraktif dan agen pempolimeran, iaitu etilena glikol selepas serbuk pelopor tersebut dikalsin pada suhu 900 °C. Sebaliknya, fasa tunggal perovskit LSC tidak terbentuk secara lengkap dalam serbuk pelopor yang disediakan dengan menggunakan surfaktan (polietilena glikol, Triton-X-100, Brij-97 dan Tween-80) walaupun selepas serbuk pelopor tersebut telah dikalsin pada suhu yang lebih tinggi iaitu 1100 °C. Kepekatan surfaktan, nisbah molar surfaktan kepada logam kation dan nilai pH larutan bahan pelopor yang tidak sesuai telah menyumbang kepada keputusan tersebut.

Effect of Bismuth Additions on Wettability, Intermetallic Compound, and Microhardness Properties of Sn-0.7Cu on Different Surface Finish Substrates

The influence of bismuth (Bi) addition on wettability, thickness of interfacial intermetallic compound (IMC), and microhardness properties of Sn-0.7Cu + xBi solder alloy using different types of substrate were examined. The 0.5, 1.0, 1.5, and 2.0 wt. % Bi was added into Sn-0.7Cu and fabricated using the casting process. The result shows that the influence of 1.5 wt. % Bi in the Sn-0.7Cu solder soldered on copper organic solderability preservative (Cu-OSP) and immersion tin (Im-Sn) surface finish has improved the wettability and microhardness. Subsequently, the IMC thickness of Sn-0.7Cu+1.5Bi solder alloy on Im-Sn surface finish gives a better result than reflowed on Cu-OSP. Generally, with the addition of 1.5 wt. % Bi in Sn-0.7Cu solder alloy reflowed on the Im-Sn surface finish had enhanced the performance in terms of wettability, thickness of IMC and microhardness properties compared to on Cu-OSP surface finish.

Bismuth Detection in Alkaline Electrolyte via Anodic Stripping Voltammetry for Battery Separator Evaluation

AbstractAnodic stripping voltammetry (ASV) has been widely used for the detection of several heavy metal ions in neutral and acidic solution, in many cases employing electrodes and/or solutions incorporating Bi. In this work we demonstrate that Bi(OH)4− ion concentration can be measured in highly alkaline 8.5 M KOH solution using ASV. The addition of Pb in similar concentrations to the Bi(OH)4− being measured is shown to improve both the sensitivity and precision of the method. When the Pb additive is employed, a formal limit of detection of 8.5 ppb is achieved, compared to 17.3 ppb when the Pb additive is not used. Due to the use of Bi additives in alkaline battery chemistries, it follows that separators which limit Bi(OH)4− diffusion into the bulk electrolyte and away from the electrodes are of interest. For this purpose, we utilize ASV to determine Bi(OH)4− diffusion rates through Celgard 3501, cellophane 350P00, and Nafion 211. Bi(OH)4− crossover rates, as determined by ASV, are shown to be repeatable and consistent with expectations from the known separator structure.

Microstructure, electrical and optical properties of NBT–xBZT lead-free single crystals

Lead-free single crystals (100-x)Na0.5Bi0.5TiO3-xBi(Zn0.5Ti0.5)O3 (x = 0, 8, 20, 30) were grown by the top seeded solution growth (TSSG) method. With the addition of Bi(Zn0.5Ti0.5)O3 (BZT), the NBT-xBZT crystals change from rhombohedral to tetragonal and the NBT-8BZT lead-free single crystals are near the morphotropic phase boundary (MPB) by studying the phase structures via X-ray powder diffraction (XRPD) and the domain structures via polarizing microscope (PLM). And with the addition of BZT, the electrical performances of NBT-xBZT crystals exhibit a trend of increasing firstly and then decreasing, in which the maximum values of piezoelectric constant d33 can be found in NBT-8BZT crystals, being 127 pC/N. The improvements of electrical performance can be attributed to the coexistence of rhombohedral and tetragonal near MPB with more possible crystallographic orientations, inducing crystals can be poled more easily, which can be verified by the piezo-response force microscopy (PFM). Furthermore, the trend of optical properties is similar to the electrical properties, in which the maximum optical transmittance is as much as 90%.

Two-dimensional Bi2OS2 doping improves the performance and stability of perovskite solar cells

• 2D Bi 2 OS 2 nanosheets are introduced as additives into the perovskite active layer. • Addition of 0.02 mg/ml 2D Bi 2 OS 2 increases power conversion efficiency (PCE) of perovskite solar cells (PVSCs). • The lifetime of optimized PVSCs is also prolonged due to addition of 2D Bi 2 OS 2 . • 2D Bi 2 OS 2 assist the formation of highly crystalline of perovskite thin film. • 2D Bi 2 OS 2 nanosheets can suppress the uncoordinated Pb 2+ ions trap states through Pb-S bond. Additive engineering has been proved to be an effective method to increase the performance of perovskite solar cells (PVSCs) by increasing the quality of the perovskite thin film. Two-dimensional (2D) Bi 2 OS 2 nanomaterial is an excellence optoelectronic material because of its tunable direct band gap, ultra-high charge mobility, wide absorption range and high absorption coefficient. In this work, 2D Bi 2 OS 2 nanosheets are synthesized and introduced as additives into the perovskite precursor solution to adjust the film formation process for the first time. Serving as heterogeneous nucleation site, 2D Bi 2 OS 2 can reduce the nucleation barrier and assist the formation of highly crystalline and crystal orientation along the (1 1 0) plane perovskite thin film, which is beneficial to improve the mobility and lifetime of charge carriers. Besides, X-ray photoelectron spectroscopy (XPS) measurement reveals that 2D Bi 2 OS 2 nanosheets can interact with Pb 2+ within the perovskite through Pb-S bond, thus suppressing the uncoordinated Pb 2+ ions trap states. Scanning electron microscope (SEM) demonstrates 2D Bi 2 OS 2 nanosheets can fill up the pin-holes and grain boundaries on the perovskite film surface. Ultraviolet photoelectron spectroscopy (UPS) measurement indicates that the valence band (VB) of optimized perovskite film is 0.28 eV upshifted closer to the highest occupied molecular orbital (HOMO) of the hole transport layer (HTL), which accelerates the charge transportation at perovskite/HTL interface. Consequently, the average power conversion efficiency (PCE) of 18.96% (highest PCE of 19.89%) is achieved upon incorporating 2D Bi 2 OS 2 nanosheets with an optimized concentration of 0.02 mg/ml into MAPbI 3 precursor solution, which is greatly improved compared to the average PCE of 15.71% for the control devices (highest PCE of 16.77%). Besides, the lifetime of optimized PVSCs is also prolonged due to the less defect states and better perovskite film quality. This work not only provides a facile method to increase the PCE and stability of PVSCs, but also reveals 2D Bi 2 OS 2 material has potential applications in PVSCs.

Influence of bismuth (Bi) addition on the structure and properties of annealed Sn-9Zn eutectic binary solder alloy

ABSTRACT The Sn-9Zn eutectic alloy has been considered as a potential replacement for toxic lead-based solders for its lower melting point (198 °C) and improved mechanical properties compared to traditional lead-based solder alloys. This paper investigates the influence of bismuth (Bi) addition as a surface-active element on the structural, thermal, mechanical, and electrical properties of eutectic Sn–9Zn alloy. Different amounts of Bi were added (x = 0.5, 1, 2, 3, wt %) to study the characteristics of Sn-9Zn-xBi ternary alloys followed by annealing at 150 °C for 60 minutes. Microstructures and phase constituents of developed alloys were examined and compared using optical microscopy and XRD respectively. The melting point and coefficient of linear thermal expansion were determined by differential thermal analysis and thermo-mechanical analysis. Tensile Properties (ultimate tensile strength, elongation, %), microhardness (HV), and electrical conductivity (% IACS) were measured. The results indicated that the addition of Bi decreased the melting point by about 10 °C, the heat of fusion, coefficient of thermal expansion, electrical conductivity than Sn-9Zn eutectic alloy. Bi addition enhanced the ultimate tensile strength and hardness by about 65% by 50% respectively. SnBi inter-metallic compound (IMC) precipitates were formed and extracted from the β-Sn matrix with a non-uniform microstructure.

Effect of Bi addition on optical properties of Se–Te–Bi films

The present paper reports the optical properties of Se80−xTe20Bix (0 ≤ x ≤ 12) films. Melt quenching method has been employed to prepare amorphous bulk samples, and thermal evaporation method has been used to deposit films of the samples under the vacuum of 10−5 torr. The structural characterization of films was carried out using X-ray diffraction and transmission electron microscopy. The X-ray diffraction studies showed that samples are amorphous in nature, while surface morphology results indicated the formation of nanorods of diameter 20–100 nm. The absorption and transmission spectra were recorded in the wavelength range 400–2500 nm, and data were used to determine refractive index, thickness of film, extinction coefficient and band gap of film samples. It was found that refractive index increases from 1.76 to 1.94 on increase in Bi wt% in the samples. Extinction coefficient also shows the same trend. This is due to increased polarizability of the larger Bi atoms. Further, the results show that energy band gap decreases on increase in Bi concentration in Se–Te–Bi nanostructured system. The value of Eg for x = 0 is 1.43 eV, while for x = 12, it decreases to 0.27 eV. The decrease in band gap is due to increase in the number of localized states, which eventually narrows the optical band gap. The values of band tail width (Ee) were also found to increase from 0.064 to 0.460 on Bi addition to Se–Te system. The small value of band gap and extinction coefficient makes these nanostructured films suitable for nano-electronic devices and anti-reflection multi layers.

Microstructural evolution and mechanical properties of binary Mg–xBi (x = 2, 5, and 8 wt%) alloys

Abstract The microstructures and mechanical properties of Mg–xBi (x = 2, 5, and 8 wt%) were investigated compared with pure Mg. The as-cast Mg–Bi billets consist of dendritic α-Mg grain matrix, divorced eutectic Mg3Bi2 phase and secondary precipitated Mg3Bi2 phase. After homogenization, secondary precipitated Mg3Bi2 particles were all dissolved into the matrix, while most of the divorced eutectic Mg3Bi2 intermetallic compounds retained. All the as-extruded samples exhibit fully dynamic recrystallization (DRX) and the average grain size decreases and the amount of nano-scale Mg3Bi2 precipitates increases with increasing Bi content. Additionally, Bi alloying has little influence on the texture of the as-extruded pure Mg, with all the samples showing typical basal texture. As the results of grain refinement and precipitation hardening, the strengths of the as-extruded samples increase under both tensile and compressive tests. Besides, the yield asymmetry significantly decreases with Bi content. Moreover, all the as-extruded samples represent similar ductility under compression, while the tensile elongation first increases and then decreases with more Bi added. The as-extruded Mg–5Bi alloy demonstrates good combination of strength and ductility. However, Mg–8Bi alloy displays lower tensile ductility than that of Mg–5Bi alloy due to the presence of abundant undissolved coarse Mg3Bi2 particles, which act as cracking sources during tensile test. Furthermore, the strain hardening rate Θ, strain hardening exponent n, and hardening capacity Hc are greatly reduced by Bi addition, mainly owing to the enhanced synergy effects of grain refinement and numerous Mg3Bi2 precipitates.

The effects of Bi and Pb on the soft phase in Al82Sn15Si2.2Cu0.8 sliding bearing alloy

Lead (Pb) is often used in AlSn based sliding bearing alloys to improve their tribological properties. However, due to the polluting and toxic nature, it is desired to replace Pb with other soft metals. Although the tribological properties of AlSn based alloy have been extensively studied, how the soft phase in alloy was influenced by alloying elements was rarely characterized. In this work, Bi is chosen for its thermodynamic similarity to Pb to investigate the effects of alloying elements on the constituents, 3D morphology, and hardness of the soft phase in AlSn based alloys. It was found that due to the immiscible characteristic with aluminum, Bi and Pb additions both tend to break the branching structure of the soft Sn-rich phase in Al82Sn15Si2.2Cu0.8 alloy and produce spherical Bi<Sn> and Pb<Sn> mixed phases respectively. It was also shown that Bi significantly increased the hardness of the Sn-rich phase by solution strengthening, but Pb has only a slight effect. The mixed phase Bi<Sn> produced by Bi addition is not softer than the Sn-rich phase in Al82Sn15Si2.2Cu0.8 alloy, but the Pb<Sn> phase produced by Pb addition is much softer. The results indicate that to replace the toxic Pb in AlSn based bearing alloys, efforts should be focused on the further reduction of the soft phase’ hardness in alloy.

Electrochemical Deposition of PdBiSn Catalyst for Glycerol Oxidation in Alkaline Medium

AbstractPdBiSn thin film on Au substrate was prepared by means of the electrochemical atomic layer deposition (E‐ALD) technique. The morphology and elemental distribution of the catalysts was determined using scanning electron microscope equipped with energy dispersive spectroscopy (EDS) detector. The catalysts contained all the deposited elements distributed evenly on the surface. Electro‐oxidation of glycerol was tested in alkaline media using cyclic voltammetry (CV) and chronoamperometry (CA). The activity of the catalysts towards the oxidation of glycerol improved with the addition of Sn and Bi with the binary PdBi catalyst being the most improved.

Structural, Thermal and Wetting Characteristics of Novel Low Bi-Low Ag Containing Sn–x.Ag–0.7Cu–1.0Bi (x = 0.5 to 1.5) Alloys for Electronic Application

Low drop failure tendency and reduced cost of low silver SAC alloys has provoked researchers to exploit their potential for portable electronics. Low Bi addition in near-eutectic SAC alloys has proven confinement of IMC layer. In order to exploit potential of Ag variation (0.5–1.5 wt%) on structural, thermal, wettability and IMCs layers growth during thermal aging in low Bi-low Ag, Sn–xAg–0.7Cu–1.0Bi alloys were investigated. The resulting microstructure were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Furthermore, structure–property correlations were established. This study signifies that 1.5 wt% Ag is responsible for lower melting point (220.18 °C) and lower contact angle (33°) in low Bi-low Ag, Sn–xAg–0.7Cu–1.0Bi alloys. Moreover, increment in Ag content restricted the interfacial IMC layer growth during thermal aging making them reliable for use in portable electronics. The microstructural investigations inferred that 0.5 wt% Ag solder joint with Cu substrate had the highest growth rate (0.34 μm/h1/2) of IMC layer thickness while 1.5 wt% Ag solder joint had lowest growth rate (0.17 μm/h1/2).

Bi(cyclopentyl)diol-Derived Boronates in Highly Enantioselective Chiral Phosphoric Acid-Catalyzed Allylation, Propargylation, and Crotylation of Aldehydes.

In this study, we disclose the catalytic addition of bi(cyclopentyl)diol-derived boronates to aldehydes promoted by chiral phosphoric acids, allowing for the formation of enantioenriched homoallylic, propargylic, and crotylic alcohols (up to >99% enantiomeric excess (ee), diastereomeric ratio (dr) >20:1). These boronate substrates provided superior enantioselectivities, allowing for the reactions to proceed with low catalyst loading (0.5-5 mol %) and reduced reaction time (15 min at room temperature for aldehyde allylboration). A wide substrate scope was exhibited, and the novel boronates provided high enantiocontrol. Reactions with substituted allylboronates and aldehydes yielded vicinal stereogenic alcohols bearing β-tertiary or quaternary carbon centers. High enantio- and diastereoselectivities were found due to the closed six-membered chair-like transition state, with backbone modifications of the boronate and its interactions with the chiral phosphoric acid being the most likely contributing factor.

The effect of Bi addition on the formation of metal whiskers in Ti2SnC/Sn-xBi system

The spontaneous growth of tin whiskers on tin-rich solders and platings has haunted the electronics industry for more than 70 years. Reliable mitigation strategies are long-waited with the proceeding of lead-free movement. However, the development of mitigation strategies has been retarded for lack of a clear whisker growth mechanism. Herein, a new research platform of Ti2SnC is developed, in which fast tin whisker growth with excellent repeatability is realized. The sample of Ti2SnC/Sn-xBi is prepared using ball-milling method, to reveal the effect of Bi addition on the growth behavior of Sn whiskers. Compared with the Ti2SnC/Sn system, an extended nucleation period is identified in Ti2SnC–Sn5Bi, Ti2SnC–Sn15Bi, Ti2SnC–Sn20Bi, which mitigates the growth of Sn whiskers in the initial stage; however, when cultivated at proper parameters, the density of Sn whiskers is found to increase with the rising of Bi content. Finally, the growth kinetics was studied using ESEM. A linear relationship between whisker length and square root of the holding time is obtained, suggesting a diffusion-controlled mechanism for the growth of Sn whiskers in this work.