Nanolevel Surface Processing of Fine Particles by Waterjet Cavitation and Multifunction Cavitation to Improve the Photocatalytic Properties of Titanium Oxide

Titanium oxide particles were treated by water jet cavitation (WJC) generated and multifunction cavitation (MFC) using an ejector nozzle. Generation, growth, and collapse of cavitation are repeated with the particles of titanium oxide and platinum. Because the cavitation has an extremely high collapse pressure, the surface of the titanium oxide particles is processed by the microjets of cavitation in a reactor comprising the ejector nozzle. In the multifunction cavitation, ultrasonic irradiation of a waterjet during floating cavitation was used to generate microjets with hot spots. Hot working can be performed at the nanoscale on a material surface using this MFC process, resulting in morphological changes and variations in the surface electrochemical characteristics. The fundamental characteristics of multifunction cavitation were investigated theoretically and experimentally. Furthermore, the additional nozzle was put on the ejector nozzle in order to increase the temperature and pressure of bubble and the mechanism was clarified. The quantities of hydrogen and oxygen generated from titanium dioxide particles treated by multifunction cavitation in response to UV and visible light irradiation were remarkably increased compared to the amounts produced by particles treated by WJC processing. In this chapter, the methods and their results of processing particles by cavitation are introduced

Indian Monsoonal Variations During the Past 80 Kyr Recorded in NGHP-02 Hole 19B, Western Bay of Bengal: Implications From Chemical and Mineral Properties

金沢大学理工研究域地球社会基盤学系Detailed reconstruction of Indian summer monsoons is necessary to better understand the late Quaternary climate history of the Bay of Bengal and Indian peninsula. We established a chronostratigraphy for a sediment core from Hole 19B in the western Bay of Bengal, extending to approximately 80 kyr BP and examined major and trace element compositions and clay mineral components of the sediments. Higher δ 18 O values, lower TiO 2 contents, and weaker weathering in the sediment source area during marine isotope stages (MIS) 2 and 4 compared to MIS 1, 3, and 5 are explained by increased Indian summer monsoonal precipitation and river discharge around the western Bay of Bengal. Clay mineral and chemical components indicate a felsic sediment source, suggesting the Precambrian gneissic complex of the eastern Indian peninsula as the dominant sediment source at this site since 80 kyr. Trace element ratios (Cr/Th, Th/Sc, Th/Co, La/Cr, and Eu/Eu*) indicate increased sediment contributions from mafic rocks during MIS 2 and 4. We interpret these results as reflecting the changing influences of the eastern and western branches of the Indian summer monsoon and a greater decrease in rainfall in the eastern and northeastern parts of the Indian peninsula than in the western part during MIS 2 and 4. © 2018. American Geophysical Union. All Rights Reserved

In-situ mechanical weakness of subducting sediments beneath a plate boundary décollement in the Nankai Trough

© 2018, The Author(s). The study investigates the in-situ strength of sediments across a plate boundary décollement using drilling parameters recorded when a 1180-m-deep borehole was established during International Ocean Discovery Program (IODP) Expedition 370, Temperature-Limit of the Deep Biosphere off Muroto (T-Limit). Information of the in-situ strength of the shallow portion in/around a plate boundary fault zone is critical for understanding the development of accretionary prisms and of the décollement itself. Studies using seismic reflection surveys and scientific ocean drillings have recently revealed the existence of high pore pressure zones around frontal accretionary prisms, which may reduce the effective strength of the sediments. A direct measurement of in-situ strength by experiments, however, has not been executed due to the difficulty in estimating in-situ stress conditions. In this study, we derived a depth profile for the in-situ strength of a frontal accretionary prism across a décollement from drilling parameters using the recently established equivalent strength (EST) method. At site C0023, the toe of the accretionary prism area off Cape Muroto, Japan, the EST gradually increases with depth but undergoes a sudden change at ~ 800 mbsf, corresponding to the top of the subducting sediment. At this depth, directly below the décollement zone, the EST decreases from ~ 10 to 2 MPa, with a change in the baseline. This mechanically weak zone in the subducting sediments extends over 250 m (~ 800–1050 mbsf), corresponding to the zone where the fluid influx was discovered, and high-fluid pressure was suggested by previous seismic imaging observations. Although the origin of the fluids or absolute values of the strength remain unclear, our investigations support previous studies suggesting that elevated pore pressure beneath the décollement weakens the subducting sediments. [Figure not available: see fulltext.]

Surface modification of Cr‒Mo steel by new technology using high speed jet in water under ultrasonic irradiation

In this study, to further improve current multifunction cavitation (MFC) techniques, the surface modification of Cr‒Mo steel was further investigated using 1200 W ultrasonic power. In MFC using 1200 W ultrasonic power, the corrosion resistance, and compressive residual stress of the specimens were improved when the processing time was 10 min; however, decarburization occurred at longer processing times, causing these characteristics to worsen. The decarburization that occurs at high ultrasonic outputs may be caused by an increase in the water temperature, and of the heating of the specimen surface

Sustainability of compressive residual stress on the processing time of water jet peening using ultrasonic power

Water jet peening (WJP) is used as a stress improvement method and a countermeasure against stress corrosion cracking (SCC) in the internal structures of reactors in nuclear power plants. However, when residual stress is converted to compressive stress and applied to the specimen surface as a countermeasure against SCC, voids and cracks can easily form inside the specimen because of the increase in the pressure applied to the surface during WJP processing. Recently, multifunction cavitation (MFC), which is WJP using ultrasonic power, has been developed as an alternative to WJP. In MFC-processed low-alloy steel, when the residual stress is converted to compressive stress as an SCC countermeasure, voids and cracks do not form inside the specimen. In this study, to further improve current MFC techniques, the surface modification of low-alloy steel (Cr–Mo steel) was further investigated using 1200 W ultrasonic power. In MFC using 1200 W ultrasonic power, the corrosion resistance, compressive residual stress, and strength of the specimens were improved when the processing time was 10 min; however, decarburization occurred at longer processing times, causing these characteristics to worsen. The decarburization that occurs at high ultrasonic outputs may be caused by an increase in the water temperature and of the heating of the specimen surface. The evaluation of the surfaces of specimens processed for 30 min at ultrasonic powers of up to 1200 W revealed that decarburization does not occur on the specimen surface as long as the power does not exceed 720 W

Processing of magnesium alloy by energy-intensive multifunction cavitation in a strong magnetic field with laser light excitation and associated sonoluminescence

This work developed a novel metal processing technique referred to as laser-assisted magnetic energy-intensive multifunction cavitation. This technology employs a strong magnetic field to focus bubble energy while applying sonic radiation around a waterjet cavitation jet. Individual bubbles in the cavitation cloud undergo repeated isothermal expansion and adiabatic compression, raising the temperature and pressure of the bubbles. In addition, the presence of a magnetic field over the region between the nozzle exit and the cavitation cloud in which cavitation primarily occurs greatly increases the number and energy density of charged bubble collisions based on the Lorentz force acting between the bubbles. The application of laser light to the charged bubble cloud provides multiphoton excitation that increases the charges of the ions within each bubble, leading to more active collisions. This enhanced cavitation treatment technology was applied to AZ31B magnesium alloy and was found to improve the functionality of the metal

New water jet cavitation technology to increase number and size of cavitation bubbles and its effect on pure Al surface

Currently, a wide variety of alloying elements are added to Al to strengthen it, which complicates the recycling process at the end of the product life. In this study, we focused on water jet cavitation (WJC) as a means to harden pure Al. When this treatment is performed, a peening effect can improve the hardness near the surface and apply a compressive residual stress, thus improving the fatigue strength. However, WJC processing requires a high-water pressure, which generally means the use of large, expensive pumps. In this study, we developed a supplemental nozzle that increases the number and size of cavitation bubbles in the discharge from a water jet nozzle. In addition, we evaluated the effect of longer WJC processing time on the pure Al surface. Conventional WJC nozzles produced erosion-forming air bubbles at the jet center. When WJC processing was performed with the new swirling flow nozzle, the increased cavitation weakened the influence of the erosion-forming bubbles. In fixed-point processing of pure Al with the new nozzle, the specimen surface underwent various cavitation erosion processes that formed a sponge-like structure, a surrounding layered structure, and detached particles. When the processing time was increased, the affected area was extended and it had more of a peened appearance. Keywords: Aluminum fatigue strength, Cavitation erosion, Swirling flow nozzle, Water jet cavitatio