High speed synchrotron X-ray imaging studies of the ultrasound shockwave and enhanced flow during metal solidification processes

The highly dynamic behaviour of ultrasonic bubble implosion in liquid metal, the multiphase liquid metal flow containing bubbles and particles, and the interaction between ultrasonic waves and semisolid phases during solidification of metal were studied in situ using the complementary ultrafast and high speed synchrotron X-ray imaging facilities housed respectively at the Advanced Photon Source, Argonne National Laboratory, US, and Diamond Light Source, UK. Real-time ultrafast X-ray imaging of 135,780 frames per second (fps) revealed that ultrasonic bubble implosion in a liquid Bi-8 wt. %Zn alloy can occur in a single wave period (30 kHz), and the effective region affected by the shockwave at implosion was 3.5 times the original bubble diameter. Furthermore, ultrasound bubbles in liquid metal move faster than the primary particles, and the velocity of bubbles is 70 ~ 100% higher than that of the primary particles present in the same locations close to the sonotrode. Ultrasound waves can very effectively create a strong swirling flow in a semisolid melt in less than one second. The energetic flow can detach solid particles from the liquid-solid interface and redistribute them back into the bulk liquid very effectively

Magnetic contrast agents for optical coherence tomography

The magneto-mechanical effect is exploited as a means of producing background-free contrast in optical coherence tomography (OCT). Contrast agents consisting of iron-oxide particles and protein microspheres encapsulating colloidal iron-oxide have a sufficiently high magnetic susceptibility to be detected by modulation of a magnetic field gradient using a small solenoid coil. The externally-applied magnetic field mechanically rotates or translates these highly scattering contrast agents within the sample at the modulation frequency, which is subsequently detected as amplitude modulation of the OCT signal. Pairs of sequential axial scans (A-lines) are acquired with the magnetic field on and off, allowing one to build up a pair of images corresponding to the "on" and "off" states of the magnetic field. These image pairs are differenced to look for magnetic-specific effects, allowing one to distinguish the magnetic contrast agents from non-magnetic structures within the sample with a signal-to-background ratio of ∼23dB. This technique has the potential to be very powerful when coupled with targeting for in vivo molecular imaging. To evaluate this potential we demonstrate in vitro imaging of magnetically-labeled macrophage cells embedded in a 3D tissue phantom, in vitro tissue doped with contrast agents, and in vivo imaging of Xenopus laevis (African frog) tadpoles

Optical characterization of contrast agents for optical coherence tomography

The use of contrast agents in almost every imaging modality has been known to enhance the sensitivity of detection and improve diagnostic capabilities by site-specifically labeling tissues or cells of interest. The imaging capabilities of Optical Coherence Tomography (OCT) need to be improved in order to detect early neoplastic changes in medicine and tumor biology. We introduce and characterize the optical properties of several types of optical contrast agents in OCT, namely encapsulating microspheres that incorporate materials including melanin, gold, and carbon. Micron-sized microspheres have been fabricated by state-of-the-art sonicating and ultrasound technology. The optical properties of optical contrast agents have been characterized according to their scattering and absorption coefficients and lifetimes using OCT and the oblique incidence reflectometry method. Finally, we demonstrate the use of these optical contrast agents in in vitro mice liver and analyze the contrast improvement from the OCT images. These optical contrast agents have the potential to improve the detection of in vivo pathologies in the future

Titania hallow-spheres for the removal of nitric oxide in air

Oxide semiconductor mediated photocatalytic purification of pollutted air and wastewater is a promising environmental remediation technology. Among various semiconductor photocatalysts, TiO2 has proven to be most suitable material for widespread environmental application due to its biological and chemical inertness, strong oxidizing power, cost efficteness, and long term stability. In this paper the possibility to use titania-hallowspheres for the removal of nitric oxide in air is presented

Porous TiO2 microspheres with tunable properties for photocatalytic air purification

The synthesis of highly-crystalline porous TiO2 microspheres is reported using ultrasonic spray pyrolysis (USP) in the presence of colloidal silica as a template. We have exploited the interactions between hot SiO2 template particles surface and TiO2 precursor that occur during reaction inside the droplets, to control the physical and chemical properties of the resulting particles. Varying the SiO2 to titanium precursor molar ratio and the colloidal silica dimension, we obtained porous titania microspheres with tunable morphology, porosity, BET surface area, crystallite size, band-gap, and phase composition. In this regard, we have also observed the preferential formation of anatase vs. rutile with increasing initial surface area of the silica template. The porous TiO2 microspheres were tested in the photocatalytic degradation of nitrogen oxides (NOx) in the gas phase. USP prepared nanostructured titania samples were found to have significantly superior specific activity per surface area compared to a commercial reference sample (P25 by Evonik-Degussa)

TiO2 hierarchical hollow microspheres with tunable properties

Recently, hierarchical hollow nanostructures (HHNs) have received a great attention for their unique or enhanced physicochemical properties [1]. Numerous strategies have been developed to synthesized TiO2 hollow nano/micro spheres, although obtaining HHNs with tunable properties remains a great scientific challenge. Here, we use ultrasonic spray pyrolysis (USP) for the generation of TiO2 hierarchical hollow spheres (HHSs) with tunable proprieties. A suspension containing colloidal silica, H2O and a TiIV complex, was nebulized using a home-made ultrasound generator (1.65 MHz). The resulting mist was carried in a gas stream in a hot furnace (1000 \ub0C). After exiting the hot zone, spherical particles a few hundred nanometers in size (microspheres) were collected in a H2O-filled bubbler [2]. The microspheres were then isolated from this solution by centrifugation and etched with HF 10 wt. % solution for 75 min. The resulting hollow nanostructure was confirmed by TEM analysis. We control the morphology of the microspheres by varying the Ti precursor/SiO2 molar ratio. In addition, by using SiO2 nanoparticles with different sizes (12, 35-50, 70-100 nm), we obtained TiO2 HHSs characterized by meso- or macroporosity. The XRD patterns of TiO2 solid spheres (obtained without tamplate, T_USP) and HHSs showed samples with dramatically different phase compositions. T_USP was composed by 36% in anatase and 64% in rutile; otherwise, by adding increasing amounts of SiO2 to the precursor solution, we obtained samples composed by an increasing content of anatase (up to 100%). We propose that the SiO2 surface play a key role in this template-directed process suggesting a possible nucleation mechanism. The photocatalytic activities of the USP microspheres have been evaluated using the NOx (gas phase) degradation as a probe reaction

Silica-directed growth of Anatase TiO2 hierarchical hollow microspheres

Recently, hierarchical hollow nanostructures (HHNs) have received a great attention for their unique or enhanced physicochemical properties1. Numerous strategies have been developed to synthesized TiO2 hollow nano/micro spheres, although obtaining HHNs with tunable properties remains a great scientific challenge. Here, we use ultrasonic spray pyrolysis (USP) for the generation of TiO2 hierarchical hollow spheres (HHSs). A suspension containing colloidal silica, H2O and a TiIV complex, was nebulized using a home-made ultrasound generator (1.65 MHz). The resulting mist was carried in a hot furnace (1000 \ub0C) by a gas (air) stream. After exiting the hot zone, spherical particles a few hundred nanometers in size (microspheres) were collected in H2O-filled bubbler2. The microspheres were then isolated from this solution by centrifugation and etched with HF 10 wt.% solution for 75 min. The resulting hollow nanostructure was confirmed by TEM analysis. We control the morphology of the microspheres by varying the Ti precursor/SiO2 molar ratio. In addition, by using SiO2 nanoparticles with different size (12, 35-50, 70-100 nm), we obtained TiO2 HHSs characterized by meso- or macroporosity. The XRD patterns of TiO2 solid spheres (obtained without template, T_USP) and HHSs showed samples with dramatically different phase composition. T_USP was composed by 36% in anatase and 64% in rutile; otherwise, by adding increasing amounts of SiO2 to the precursor solution, we obtained samples composed by an increasing content of anatase (up to 100%). We propose that the SiO2 surface plays a key role in this template-directed process (figure) suggesting a possible nucleation mechanism. The photocatalytic activities of the USP microspheres have been evaluated using the NOx (gas phase) degradation as a probe reaction