Engineering topics
Liu, Chunming
Publications and source records attributed to Liu, Chunming.
Super-resolution imaging of non-fluorescent reactions via competition
Super-resolved fluorescence microscopy techniques have enabled substantial advances in the chemical and biological sciences. However, they can only interrogate entities that fluoresce, and most chemical or biological processes do not involve fluorescent species. Here we report a competition-enabled imaging technique with super-resolution (COMPEITS) (a COMPetition-Enabled Imaging Technique with Super-resolution) that enables quantitative super-resolution imaging of non-fluorescent processes. It is based on the incorporation of competition into a single-molecule fluorescence-detection scheme. We demonstrate COMPEITS by investigating a photoelectrocatalytic reaction; we map, with nanometre precision, a non-fluorescent surface reaction that is important for water decontamination on single photocatalyst particles. The subparticle-level quantitative information of reactant adsorption affinities unambiguously decouples size- and shape-scaling laws on specific particle facets and uncovers a surprising biphasic shape dependence, leading to catalyst design principles for optimal reactant adsorption efficacy. With its ability to provide spatially resolved information on the behaviours of unlabelled, non-fluorescent entities under operando conditions, COMPEITS could interrogate a variety of surface processes in fields ranging from heterogeneous catalysis and materials engineering to nanotechnology and energy sciences.
Effect of Tempering Temperature on the Precipitation Behavior and Mechanical Properties of a Martensite Ferritic Steel
In this investigation, the precipitation of boron-containing M{sub 23}C{sub 6} in the CB2 steel during tempering was investigated. Scanning electron microscopy, energy-dispersive x-ray spectroscopy, transmission electron microscopy and differential scanning calorimetry were used to analyze the influence of temperature on the microstructure and properties of CB2-tempered martensite ferritic steel. The steel was normalized at 1100 °C for 2 h and then tempered at six different temperatures between 690 and 790 °C for 2 h. During air-cooling following austenitization, the precipitation of M{sub 3}C particles occurred in flakes forming with their diameter and thickness of 100 and 20 nm, respectively. The boron-containing M{sub 23}C{sub 6} was formed on the lath boundary after the dissolution of M{sub 3}C within the boundary. When the tempering temperature increased from 690 to 790 °C, the average diameter of boron-containing M{sub 23}C{sub 6} increased from 132 to 198 nm. Owing to the rapid growth of the precipitates, the phenomenon of lath widening as well as the recovery of microstructure would take place at high temperature. With an increase in the temperature, the tensile and yield strengths decreased gradually, while the plasticity increased and the boron-containing M{sub 23}C{sub 6} grew rapidly. Furthermore, when the tempering temperature exceeded 750 °C, the plasticity of CB2 steel was significantly improved.
Tuning Optical and Electronic Properties in Low-Toxicity Organic–Inorganic Hybrid (CH 3 NH 3 ) 3 Bi 2 I 9 under High Pressure
Low-toxicity, air-stable methylammonium bismuth iodide (CH 3 NH 3 ) 3 Bi 2 I 9 has been proposed as a candidate to replace lead-based perovskites as highly efficient light absorbers for photovoltaic devices. Here, we investigated the effect of pressure on the optoelectronic properties and crystal structure of (CH 3 NH 3 ) 3 Bi 2 I 9 up to 65 GPa at room temperature. We achieved impressive photoluminescence enhancement and band gap narrowing over a moderate pressure range. Dramatic piezochromism from transparent red to opaque black was observed in a single crystal sample. A structural phase transition from hexagonal P6 3 / mmc to monoclinic P21 at 5.0 GPa and completely reversible amorphization at 29.1 GPa were determined by in situ synchrotron X-ray diffraction. Moreover, the dynamically disordered MA + organic cations in the hexagonal phase became orientationally ordered upon entering into the monoclinic phase, followed by static disorder upon amorphization. The striking enhancement of conductivity and metallization under high pressure indicate wholly new electronic properties.
Effect of Y/Ti atomic ratio on microstructure of oxide dispersion strengthened alloys
Highlights: • Controlling nano oxide distributions in ODS alloys by tuning Y/Ti ratio. • Advanced characterization techniques have been conducted to comprehensively study the various nano oxides. • A recipe with a Y/Ti ratio of 0.4 was found and the intrinsic oxide formation mechanism was explained. - Abstract: Oxide dispersion strengthened (ODS) alloys are the leading candidate materials for advanced fission and fusion reactor components because of their excellent high temperature creep strength and radiation tolerance. The promising performance of ODS alloys relies on a high-density population of nano oxides. Here, four 9Cr-ODS alloys with varying initial Y/Ti atomic ratio were processed using a combined route of mechanical alloying (MA) and hot isostatic pressing (HIP). Microstructural characterizations of the consolidated alloys were examined by advanced transmission electron microscopy (TEM). Great differences in oxide distribution behavior were observed. 9Cr-ODS alloy with a Y/Ti ratio of 0.4 presented the finest and the highest number density of nano oxides among the four alloys. The effects of Y/Ti ratio on oxide formation were explored, and the precipitated mechanisms of the nano oxides were interpreted.