Wubian Tian

Spontaneous Sn whisker formation on Ti2SnC

Spontaneous Sn whisker growth on Sn-containing substrates has resisted interpretation for several decades. In this paper, Ti2SnC-Sn and Ti2SnC samples were prepared and then cultivated in the same conditions. Many Sn whiskers had appeared on the ball milled Ti2SnC-Sn sample after being stored in air for 40xa0days, while no whisker grew on the Ti2SnC-Sn samples without ball milling although the cultivation time had been extended to more than half a year. Moreover, even though it was ball milled, the Sn-free Ti2SnC sample did not grow any whisker. The whiskers formed on this system share typical features with the ones grown on Sn platings and solders, while they do not follow any of the existing growth models. A catalysis-based whisker formation model, in which the cleavage planes of Ti2SnC grains act as heterogeneous nucleation sites, is proposed, which well interprets Sn whisker formation in the ball milled Ti2SnC-Sn system.

Fabrication of Lithiophilic Copper Foam with Interfacial Modulation toward High-Rate Lithium Metal Anodes

Although metallic lithium is regarded as an ideal anode material for high-energy-density batteries, the low cycling efficiency and safety issues hinder its practical application. In this study, a three-dimensional (3D) lithium composite anode was developed through infusing molten lithium inside the Cu foam anchored by ZnO nanoparticles. The introduced ZnO layer provides the driving force for infusion, leading to the spontaneous wetting of molten lithium. Benefiting from well-confined preloaded lithium in the Cu network, the anode displays ultralow internal resistance and stabilized interface. The fabricated anode for the symmetric cell shows extraordinarily low overpotential at high current densities (15, 33, and 50 mV at 3, 5, and 8 mA cm-2 after 100 cycles, respectively). When paired with Li4Ti5O12 electrode, the half-type cell demonstrates superior rate capability and long-term cycling stability after 1000 cycles at an ultrahigh rate of 10C. To the best of our knowledge, this anode shows the lowest overpotential and the highest rate capacity ever reported for 3D design anodes, confirming their great potential as lithium metal anodes.

Preparation and properties of thermal insulation coatings with a sodium stearate-modified shell powder as a filler

Waste shell stacking with odor and toxicity is a serious hazard to our living environment. To make effective use of the natural resources, the shell powder was applied as a filler of outdoor thermal insulation coatings. Sodium stearate (SS) was used to modify the properties of shell powder to reduce its agglomeration and to increase its compatibility with the emulsion. The oil absorption rate and the spectrum reflectance of the shell powder show that the optimized content of SS as a modifier is 1.5wt%. The total spectrum reflectance of the coating made with the shell powder that is modified at this optimum SS content is 9.33% higher than that without any modification. At the optimum SS content of 1.5wt%, the thermal insulation of the coatings is improved by 1.0°C for the cement mortar board and 1.6°C for the steel plate, respectively. The scouring resistance of the coating with the 1.5wt% SS-modified shell powder is three times that of the coating without modification.

Pretreatment on Ti substrate for Ti/Pt anode by electrolytic plasma processing

ABSTRACT The electrolytic plasma processing (EPP) process was employed to pretreat Ti substrates before applying Pt coating rather than using the conventional pickling route, resulting in increased efficiency and reduced environmental hazard. The successive anode-cathode EPP and single cathode EPP were used to pretreat the Ti substrate, respectively, and then the Ti/Pt anodes were prepared by the dip-coating/calcination method. The composition, morphology and electrochemical properties were investigated by X-ray diffraction, scanning electron microscopy and electrochemical workstation, respectively. The results show that the successive anode-cathode EPP-treated Ti substrate has uniform micro/nano-scale surface structure, and its corresponding Ti/Pt anode has the lowest impedance and best electrocatalytic activity among the Ti/Pt anodes prepared in this work.

Effect of temperature on the mechanical behavior of B4C joints bonded by Al infiltrated TiC tape

B4C ceramics has potential applications at moderately elevated temperatures (<u2009450xa0°C) for semiconductor industry and solar systems due to their high elastic modulus and stability. B4C sintered bodies were joined by Al infiltrated TiC tape at 1000xa0°C for 0.5xa0h in vacuum. The mechanical properties in the 20–600xa0°C temperature range were investigated. B4C joints (267xa0MPa) show comparable mechanical properties to B4C matrix (271xa0MPa) at room temperature according to Weibull analysis. The bending strength of B4C joint maintains to be about 250xa0MPa up to 500xa0°C and then decreases quickly with further increasing temperature. Microstructural observations on fracture surface suggest that the high-temperature strength is dominated by the softening of Al binder phase in the interlayer.

Toward advanced sodium-ion batteries: a wheel-inspired yolk–shell design for large-volume-change anode materials

Yolk–shell structures have found great potential in addressing the huge volume change of alloy-type anodes for lithium-/sodium-ion batteries (LIBs/SIBs). The main challenges associated with yolk–shell structures are the sluggish electron/ion transfer at the yolk–shell interface caused by the point-to-point contact between the yolk and the shell, and the rupture of self-supporting carbon shells during a long-term cycle. Here, inspired by the structure of a wheel, we designed and fabricated a novel yolk–shell structure with a multipoint contact between the yolk and the shell (wheel–shell structure) through a general and scalable approach. The multipoint contact is achieved by bridging SnO2 yolks and graphene shells using carbon nanoribbons, which allows a high-efficiency transfer of electrons and ions inside/outside the wheel–shell structure. Moreover, the interconnected graphene shells function not only as an electrical highway so that all active materials are electrochemically active, but also as a mechanical backbone to maintain the structural integrity. As an anode for SIBs, the wheel–shell structure exhibits extraordinary rate capability (153.3 mA h g−1 at 10.0 A g−1) and robust cycling stability (248.2 mA h g−1 remaining after 1000 cycles at 1.0 A g−1 with a capacity retention of 86.9%). These results demonstrate the most efficient SnO2-based anode ever reported for SIBs. More importantly, the proposed strategy opens up new avenues to boost the electrochemical performance of large-volume-change anode materials for advanced battery systems.

Synthesis and formation mechanism of titanium lead carbide

Ti2PbC was synthesized for the first time by pressureless reaction synthesis using Ti/Pb/TiC as starting materials at a heating rate of 2 °C/min and holding at 1370 °C for 2 h in a tube furnace protected by Ar atmosphere. The effects of starting powders, heating rates, and holding temperatures on the formation of Ti2PbC were investigated. It was found that elementary mixture of Ti/Pb/C or higher heating rates fail to form Ti2PbC. The decreased lattice parameters in the synthesized Ti2PbC indicated the existence of Pb vacancies in the compound. A reaction mechanism was proposed to explain the formation of Ti2PbC.

Microstructure and properties of Ag–Ti3SiC2 contact materials prepared by pressureless sintering

Ti3SiC2-reinforced Ag-matrix composites are expected to serve as electrical contacts. In this study, the wettability of Ag on a Ti3SiC2 substrate was measured by the sessile drop method. The Ag–Ti3SiC2 composites were prepared from Ag and Ti3SiC2 powder mixtures by pressureless sintering. The effects of compacting pressure (100–800 MPa), sintering temperature (850–950°C), and soaking time (0.5–2 h) on the microstructure and properties of the Ag–Ti3SiC2 composites were investigated. The experimental results indicated that Ti3SiC2 particulates were uniformly distributed in the Ag matrix, without reactions at the interfaces between the two phases. The prepared Ag–10wt%Ti3SiC2 had a relative density of 95% and an electrical resistivity of 2.76 × 10-3 mΩ·cm when compacted at 800 MPa and sintered at 950°C for 1 h. The incorporation of Ti3SiC2 into Ag was found to improve its hardness without substantially compromising its electrical conductivity; this behavior was attributed to the combination of ceramic and metallic properties of the Ti3SiC2 reinforcement, suggesting its potential application in electrical contacts.

Brazing of silicon carbide ceramics with Ni-Si-Ti powder mixtures

In many industrial applications, large-sized SiC components are increasingly desired through a conventional and pressureless brazing method. In present study, Ni-Si-Ti powder mixtures containing 0~10xa0wt.% Ti were used to braze SiC ceramics. Differential thermal analysis (DTA) and wetting tests were carried out to determine the appropriate joining temperature to be at 1450xa0°C. Microstructure, phase constituents, and mechanical strength of the prepared SiC joints were characterized. For a brazing composition without Ti addition, the interlayer primarily consists of NiSi and Ni3Si2 phases. With the addition of Ti, Ni49Ti14Si37 phase is newly formed within the interlayer besides the Ni-Si compounds. The bending strengths of SiC joints locate in 66~75xa0MPa as brazed at present conditions and the specimens generally fracture from the interface between alloy interlayer and SiC substrate.

Dual Electrolytic Plasma Processing for Steel Surface Cleaning and Passivation

To remove the rust on rebars and passivate the fresh surfaces, electrodes reversing electrolytic plasma processing (EPP) was proposed and conducted in a 10xa0wt.% Na2CO3 aqueous solution. The morphology and the composition of the surface were investigated by SEM and XPS. Experimental results show that the rust on the surface was removed effectively by cathode EPP, and a passive film containing Cr2O3 was achieved by the succeeding anode EPP treatment, by a simple operation of reversing the bias. The corrosion resistance was evaluated in a 3.5xa0wt.% NaCl aqueous solution using an electrochemical workstation. In comparison, the corrosion resistance was improved by the succeeding anode EPP treatment, which is evidenced by a positive shift of the open-circuit potential, an increase in the electrochemical impedance representing the inner layer by 76.8% and the decrease in the corrosion current density by 49.6%. This is an effective and environment-friendly technique to clean and passivate rebars and similar steel materials.