Coarsening behavior of bulk nanobubbles in water

In recent years, minuscule gas bubbles called bulk nanobubbles (BNBs) have drawn increasing attention due to their unique properties and broad applicability in various technological fields, such as biomedical engineering, water treatment, and nanomaterials. However, questions remain regarding the stability and behavior of BNBs. In the present work, BNBs were generated in water using a gas–liquid mixing method. NB analysis was performed using a nanoparticle tracking analysis (NTA) method to investigate the coarsening behavior of BNBs in water over time. The diameters of the BNBs increased, and their cubic radii increased linearly (r3 ~ t) over time. While the concentration of BNBs decreased, the total volume of BNBs remained the same. The size distribution of the BNBs broadened, and the concentration of larger BNBs increased over time. These results indicate that relatively small BNBs disappeared due to dissolution and larger BNBs grew through mass transfer between BNBs instead of coalescence. In other words, BNBs underwent Ostwald ripening: gas molecules from smaller BNBs diffused through the continuous phase to be absorbed into larger BNBs.

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.

The Effect of Aging on Precipitates, Mechanical and Magnetic Properties of Fe-21Cr-15Ni-6Mn-Nb Low Magnetic Stainless Steel

The effect of aging on the precipitates, mechanical and magnetic properties of Fe-21Cr-15Ni-6Mn-Nb low magnetic stainless steel were investigated. The steel was aged at 550–750 °C for 2 h after solution heat treatment at 1100 °C for 1 h. During the aging treatment, the (Nb, V)(C, N) particles gradually precipitated in the grain, which were coherent or semi-coherent with the matrix. When the aging temperature was beyond 650 °C, the coarsening rate of (Nb, V)(C, N) particles increase rapidly and the coherent orientation between (Nb, V)(C, N) particles and the matrix was lost gradually. Meanwhile, coarse M23C6 was distributed at the grain boundary with chain shape, which was non-coherent with the matrix. The coarsening behavior of (Nb, V)(C, N) precipitates in the grain was analyzed, and the size of the particles precipitated after aging treatment at 650°C for different time was calculated and studied. After aging treatment at 650 °C for 2 h, the yield strength and tensile strength of the stainless steel was 705.6 MPa and 1002.3 MPa, the elongation and the relative magnetic permeability was 37.8% and 1.0035, respectively.