TEM Characterization of Helium Bubbles in T91 and MNHS Steels Implanted with 200 keV He Ions at Different Temperatures

Modified novel high silicon steel （MNHS, a newly developed reduced-activation martensitic alloy） and commercial alloy Tgl are implanted with 200 keV He2＋ ions to a dose of 5 × 1020 ions/m2 at 300, 450 and 560~C. Transmission electron microscopy （TEM） is used to characterize the size and morphology of He bubbles. With the increase of the implantation temperature, TEM observations indicate that bubbles increase in size and the proportion of ＇brick shaped＇ cuboid bubbles increases while the proportion of polyhedral bubbles decreases in both the steel samples. For the samples implanted at the same temperature, the average size of He bubbles in MNHS is smaller than that in T91. This might be due to the abundance of boundaries and precipitates in MNHS, which provide additional sites for the trapping of He atoms, thus reduce the susceptibility of MNHS to He embrittlement.

Characterization and degradation of β-Sn particles in thermal aged Pb-rich solder joint for low-temperature co-fired ceramic(LTCC)applications

High-lead solder joints are still playing an indispensable role in military and space applications.Nevertheless,in-depth characterization of high-lead solder joints and the underlying degradation mechanisms remain unexplored.This research first performed aging tests on Sn10Pb90 solder joints,the shear strength at room and elevated temperatures gradually reduced,and the resistance increased.Here,a two-layered Ni-Sn intermetallic compound(IMC)structure was identified using transmission electron microscopy(TEM),which could be attributed to the change of Sn content in the solder.Moreover,the internal annealing twin of a Sn particle was discovered,which could be attributed to creeping induced by thermal expansion coefficient(CTE)difference between Sn and Pb.Detailed analysis of partial and whole annealing twins was conducted through high-resolution TEM(HRTEM).Finally,four degradation mechanisms were proposed.Thickening of the IMC layer would result in increased brittleness and resistivity.For particle coarsening,apart from diminishing the ductility and toughness of the solder joint,it would also accelerate the creeping rate by weakening the phase boundary strength.Regarding voids and cracks induced by phase boundary sliding,wedgeshaped cracking and pore-shaped cracking were discovered and their formation was analyzed.Most importantly,the consumption of Sn resulted in a depletion of wettable layer,leading to the formation of Pb streams and isolated IMC islands,also known as the spalling and delamination of IMCs.Pb diffusion followed a spiral path,which was mutually influenced by orientation misfit and concentration gradient.A technique to prevent cracking was proposed.This research is expected to provide significant technical references for high-lead solder joints.

Ternary Pt/Re/SnO2/C catalyst for EOR:Electrocatalytic activity and durability enhancement

Carbon-supported Pt/C,Pt/Re/C,Pt/SnO2/C and Pt/Re/SnO2/C,with 20 wt.%overall metal loading were prepared and their electrochemical activity towards ethanol oxidation reaction(EOR)was investigated.Transmission electron microscopy(TEM)combined with energy dispersive X-ray spectroscopy(EDS)revealed,that indeed binary and ternary combinations of the designed nanoparticles(NPs)were formed and successfully uniformly deposited on a carbon support.Fourier transform infrared spectroscopy(FTIR)allowed to assess the chemical composition of the nanocatalysts and X-ray diffraction(XRD)allowed to determine the catalyst structure.Potentiodynamic and chronoamperometric measurements were used to establish its catalytic activity and stability.The influence of Re addition on the electrochemical activity towards ethanol oxidation reaction(EOR)was verified.Indeed,the addition of Re to the binary Pt/SnO2/C catalyst leads to the formation of ternary Pt/Re/SnO2/C with physical contact between the individual NPs,enhancing the EOR.Furthermore,the onset potential of the synthesized ternary catalyst is shifted to more negative potentials and the current densities and specific activity are nearly 11 and 5 times higher,respectively,than for commercial Pt catalyst.Additionally ternary Pt/Re/SnO2/C catalyst retained 96%of its electrochemical surface area.

Advanced Transmission Electron Microscopy for Identification of Atomic-Scale Configurations of Zeolite-Supported Metal Catalysts

Zeolite-supported metal catalysts have important applications in various catalytic reactions,but unveiling their atomic-scale structures is always a grand challenge.The developed transmission electron microscopy(TEM)characterization techniques,e.g.,integrated differential-phase contrast(iDPC)scanning transmission electron microscopy(STEM)is emerging as a powerful tool for visualizing the electron beam-sensitive materials at atomic resolution,thus,providing new opportunities for imaging the exact configurations of metal species in the various channels of zeolites.This emerging topic summarizes recent progress utilizing iDPC-STEM-related technique for determination of the structures of metal species in zeolites that should offer insights into the structure-property relationships of zeolite-supported metal catalysts.A brief perspective about the new TEM technique is also presented,showing prospects in this field that will stimulate further scientific research in zeolite-supported metal catalysts.

Synthesis of Single-Crystal TiO_2 Nanowire Using Titanium Monoxide Powder by Thermal Evaporation

TiO 2 nanowires were synthesized successfully in a large quantity by thermal evaporation using titanium monoxide powder as precursor. X-ray diffraction results showed that all the products were pure rutile phase of TiO 2 . According to microstructural observations, the nanowires have two typical morphologies, a long straight type and a short tortuous type. The straight nanowires were obtained at a wide temperature range of 900–1050 ℃, while the tortuous ones were formed below 900 ℃. Transmission electron microscopy characterization revealed that both the straight and the tortuous nanowires are single-crystal rutile TiO 2 . The preferential growth direction of the nanowires was determined as [110] orientation according to electron diffraction and high-resolution image analyses. The morphological change of TiO 2 nanowires was discussed by considering the different atomic diffusion rates of Ti atoms caused by the phase transformation in Ti substrate at around 900 ℃.