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.

Mechanical Strength and Hydration Characteristics of Cement Mixture with Highly Concentrated Hydrogen Nanobubble Water.

In this study, highly concentrated hydrogen nanobubble water was utilized as the blending water for cement mortar to improve its compressive and flexural strengths. Highly concentrated nanobubbles can be obtained through osmosis. This concentration was maintained by sustaining the osmotic time. The mortar specimens were cured for 28 days, in which the nanobubble concentration was increased. This improved their flexural strength by 2.25-13.48% and compressive strength by 6.41-11.22%, as compared to those afforded by plain water. The nanobubbles were densified at high concentrations, which caused a decrease in their diameter. This increased the probability of collisions with the cement particles and accelerated the hydration and pozzolanic reactions, which facilitated an increase in the strength of cement. Thermogravimetric analysis and scanning electron microscopy were used to confirm the development of calcium silicate hydrate (C-S-H) and hydration products with an increase in the nanobubble concentration. Quantitative analysis of the hydration products and the degree of hydration were calculated by mineralogical analysis.

Effect of Hydrogen Nanobubbles on the Mechanical Strength and Watertightness of Cement Mixtures.

This study analyzed the effects of applying highly concentrated hydrogen nanobubble water (HNBW) on the workability, durability, watertightness, and microstructure of cement mixtures. The number of hydrogen nanobubbles was concentrated twofold to a more stable state using osmosis. The compressive strength of the cement mortar for each curing day was improved by about 3.7-15.79%, compared to the specimen that used general water, when two concentrations of HNBW were used as the mixing water. The results of mercury intrusion porosimetry and a scanning electron microscope analysis of the cement paste showed that the pore volume of the specimen decreased by about 4.38-10.26%, thereby improving the watertightness when high-concentration HNBW was used. The improvement in strength and watertightness is a result of the reduction of the microbubbles' particle size, and the increase in the zeta potential and surface tension, which activated the hydration reaction of the cement and accelerated the pozzolanic reaction.

Characteristics of CO2 and Energy-Saving Concrete with Porous Feldspar.

In this study, to reduce the use of cement and sand, porous feldspar with excellent economic efficiency was used as a substitute in the heat storage concrete layer. When porous feldspar and four other silicate minerals were used as substitute materials for sand in cement mortar, the specimen with the porous feldspar exhibited approximately 16-63% higher compressive strength, thereby exhibiting a higher reactivity with cement compared to the other minerals. To compensate for the reduction in strength owing to the decreased cement content, mechanical and chemical activation methods were employed. When the specific surface area of porous feldspar was increased, the unit weight was reduced by approximately 30% and the compressive strength was increased by up to 90%. In addition, the results of the thermal diffusion test confirmed that thermal diffusion increased owing to a reduction in the unit weight; the heat storage characteristics improved owing to the better porosity of feldspar. When chemical activation was performed after reducing the cement content by 5% and replacing the sand with porous feldspar, the compressive strength was found to be approximately twice that of an ordinary cement mortar. In a large-scale model experiment, the heat storage layer containing the porous feldspar exhibited better heat conduction and heat storage characteristics than the heat storage layer composed of ordinary cement mortar. Additionally, energy savings of 57% were observed.

An Experimental Study on Bubble Collapsing Effect of Nanobubble Using Ultrasonic Wave.

The nanobubbles generated in water are large in non-surface aspect that allows the formation of radicals on their surface. Nanobubbles maintain high pressure inside, and are capable of Brownian motion Most of nanobubbles based research focused on the characteristic of nanobubble to maintain high pressure inside while it shrunk. High temperature was generated when bubble was collapsed by an external impact. In this study, hydrogen nanobubbles were produced based on a self-technique that could store nanobubbles for a long period. The test was conducted to destroy nanobubbles in hydrogen nanobubble water. Ultrasonic waves were applied into the water to destroy nanobubbles and there was rise in water temperature, which was caused by the collapsing effect of bubbles. When ultrasonic waves were applied, the collapsing effect of bubbles was largely exhibited within the initial one minute of the experiment. It was confirmed that the wattage of ultrasonic wave was significantly affected. If the collapsing effect of nanobubbles can be measured, it will be possible to apply this method positively to various fields.

Compressive Strength Evaluation of Ordinary Portland Cement Mortar Blended with Hydrogen Nano-Bubble Water and Graphene.

Abnormal climate changes have occurred all over the world due to greenhouse gases (GHGs). Various countries are targeting emission reductions of GHGs in 2020 and trying to GHGs those in multiple fields. Cement-based structures account for a large part in the construction industry. One ton of carbon dioxide is produced during the manufacturing process for a ton of cement. Therefore, decreasing cement usage is essential for carbon dioxide reduction. However, strength characteristics of cement are necessary conditions to meet the required strength of a structure. Therefore, it is necessary to develop cement substitutes and economic additives. In this study, we proposed an eco-friendly blend ratio by comparing the compressive strength of Ordinary Portland Cement (OPC) mortar and two variations. One was a mortar with a small amount of APTMS-sGO added. The other was a mortar mixed with HNBW (hydrogen nano-bubble water) as an enhanced material instead of ordinary water. The mortar added with 0.1% of APTMS-sGO showed improved early strength compared with OPC mortar. Its strength was enhanced 31.1% by using HNBW as functional water. Strength was improved 20.4% for cement mortar added with Graphene Oxide after reacting with SAM containing APTMS. When the texture of both mortars became denser, early compressive strength at 7 days each was 20.4-31.1% higher than that of OPC mortar. Finally, the strength was increased by 10.2% at 28 days.

Enhanced electrokinetic (E/K) remediation on copper contaminated soil by CFW (carbonized foods waste).

The E/K remediation method is presented to purify low permeable contaminated soils due to Cu(2+), and carbonized foods waste (CFW) was used as a permeable reactive barrier (PRB) material. For adsorption and precipitation of the Cu(2+) in the PRB during its motion, PRB was installed in a zone of rapidly changing pH values. The adsorption efficiency of CFW used as PRB material was found to be 4-8 times more efficient than that of Zeolite. Throughout the experiment, a voltage slope of 1V/cm was implemented and acetic acid was injected on the anode to increase the remediation efficiency. The electrode exchange was executed to more completely remove precipitated heavy metals in the vicinity of the cathode. The majority of Cu(2+) was adsorbed or sedimented by CFW prior to the exchange of the electrode, and the remaining quantity of precipitated Cu(2+) on the cathode had decreased with an increase in the operating time. Experiments of seven cases with different E/K operating times were performed, and the average removal ratios were 53.4-84.6%. The removal efficiencies for the majority of cases increased proportionally with an increase in the operating time. After the experiments were completed, the adsorbed Cu(2+) on CFW was 75-150 mg. This means that the role of CFW as the material in PRB for remediating heavy metals was confirmed. The cost of energies needed to remove Cu(2+), CFW, and acetic acid are estimated at US$ 13.3-40/m(3).