Coarsening Behavior of Bulk Nanobubbles in Water

In recent years, extremely small gas bubbles called bulk nanobubbles (BNBs) have drawn great attention due to their impressive effects and their wide applicability in a variety of technological fields, including biomedical engineering, water treatment, and nanomaterials. However, unsolved questions remain regarding the stability and behavior of BNBs. In the present work, BNBs were generated in water using a gas-liquid mixing method. To investigate the coarsening behavior of BNBs in water over time, particle analysis was performed using a nanoparticle tracking analysis (NTA) method. Over time, the BNB diameter continuously increased (from 88.50 nm to 201.00 nm), and its cubic radius increased linearly (r3 ~ t). While the concentration of BNBs decreased (from 3.47 ×108 particles/mL to 0.61 ×108 particles/mL), the total volume of BNBs remained the same. Moreover, the size distribution broadened over time, and the concentration of larger BNBs gradually increased over time. These results indicate that relatively small BNBs disappear and larger BNBs grow through mass transfer between BNBs instead of dissolution of the gas and coalescence. In other words, BNBs underwent Oswald ripening; that is, gas molecules detached from smaller BNBs, diffused into the continuous phase, and then were absorbed into larger BNBs.

Phase evolution and structural modulation during in situ lithiation of MoS2, WS2 and graphite in TEM

Li-ion batteries function by Li intercalating into and through the layered electrode materials. Intercalation is a solid-state interaction resulting in the formation of new phases. The new observations presented here reveal that at the nanoscale the intercalation mechanism is fundamentally different from the existing models and is actually driven by nonuniform phase distributions rather than the localized Li concentration: the lithiation process is a ‘distribution-dependent’ phenomena. Direct structure imaging of 2H and 1T dual-phase microstructures in lithiated MoS2 and WS2 along with the localized chemical segregation has been demonstrated in the current study. Li, a perennial challenge for the TEM, is detected and imaged using a low-dose, direct-electron detection camera on an aberration-corrected TEM and confirmed by image simulation. This study shows the presence of fully lithiated nanoscale domains of 2D host matrix in the vicinity of Li-lean regions. This confirms the nanoscale phase formation followed by Oswald ripening, where the less-stable smaller domains dissolves at the expense of the larger and more stable phases.

A Computational Method for The Computer Simulation of The Liquid Phase Sintering of Metallic Systems

The growth of solid particles during liquid phase sintering was modeled by the Cellular Automata method. The binary phase diagram and Fickian approach for the diffusion process were applied to simulate the chemical composition variation in liquid and solid phases during sintering. The Oswald-Ripening effect was considered during the dissolution of the solid phase in the liquid phase. It is used to define the probability of solid-phase dissolution by the liquid phase and develop the model to simulate the alloy with solid solubility. So, the microstructure could be modeled in the liquid phase sintering process.

Real-time atomistic simulation of the Ostwald ripening of TiO2 supported Au nanoparticles

Atomic simulation shows a stagewise Oswald Ripening with changing rate-determining step. In the ripening, the particles exchange dimers among each other instead of monomers.

Synthesis of Metallic Nanocrystals: From Noble Metals to Base Metals

Metallic nanocrystals exhibit superior properties to their bulk counterparts because of the reduced sizes, diverse morphologies, and controllable exposed crystal facets. Therefore, the fabrication of metal nanocrystals and the adjustment of their properties for different applications have attracted wide attention. One of the typical examples is the fabrication of nanocrystals encased with high-index facets, and research on their magnified catalytic activities and selections. Great accomplishment has been achieved within the field of noble metals such as Pd, Pt, Ag, and Au. However, it remains challenging in the fabrication of base metal nanocrystals such as Ni, Cu, and Co with various structures, shapes, and sizes. In this paper, the synthesis of metal nanocrystals is reviewed. An introduction is briefly given to the metal nanocrystals and the importance of synthesis, and then commonly used synthesis methods for metallic nanocrystals are summarized, followed by specific examples of metal nanocrystals including noble metals, alloys, and base metals. The synthesis of base metal nanocrystals is far from satisfactory compared to the tremendous success achieved in noble metals. Afterwards, we present a discussion on specific synthesis methods suitable for base metals, including seed-mediated growth, ligand control, oriented attachment, chemical etching, and Oswald ripening, based on the comprehensive consideration of thermodynamics, kinetics, and physical restrictions. At the end, conclusions are drawn through the prospect of the future development direction.

Modeling of the Hot Rolling: Towards the Industrial Applicability

A semi-empirical approach to the modeling of the microstructural evolution during the hot rolling of austenite including grain growth, hardening and softening has been discussed in the frame of a generalized energetic expression for related structural processes. The current concept suggests the activation energy of iron self-diffusion in austenite and its dependence upon the chemical composition of the steel for prediction of the particular phenomena. Additionally, the precipitation sequences, the size distribution, Oswald ripening and interaction with softening are also included in the model of the microstructural evolution. The simulation results are reliable to the structural evolution of the low carbon steels microalloyed with Nb and Ti during hot rolling.

Asymmetric AgPd–AuNR heterostructure with enhanced photothermal performance and SERS activity

A general approach is proposed for the first time for the fabrication of an asymmetric AgPd–AuNR heterostructure with an enhanced photothermal heating performance and SERS activity through a galvanic replacement reaction and an Oswald ripening process.

Study of Nano-Precipitate in High Strength Low Carbon Steel during Tempering by TEM

The behavior of nanoprecipitates of 800Mpa grade high strength low carbon steel during tempering has been studied. Transmission electron microscope (TEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive spectrometry (EDS) were used to systematically analyze the morphology of precipitates and their grain orientation with matrix at different tempering temperatures. Experimental results confirm that the composition of these nanometer sized particles in the matrix was compound carbonitrides containing Ti, V, Mo and other elements. The precipitates of the as-received steel are (Nb,Ti)(C,N) at low tempering temperature, while those at high tempering temperature are composite carbides containing a variety of elements such as Mo, V, Ti and Nb. On the other hand, as tempering temperature increases, precipitates in the steel were slowly growing up and roughening according with the typical Oswald ripening mechanism; a sharp orientation relationship exists between precipitates and matrix.