Electrochemical behavior of Ti-6.5Al-2Zr-1Mo-1V alloy under rotating condition with periodically fluctuating current density

Titanium alloy plays a crucial role in the electrochemical field due to its excellent corrosion resistance.The passivation and dissolution behaviors of Ti-6.5Al-2Zr-1Mo-1V(TA15)alloy in Na Cl solution were studied by simulating the electrochemical machining process in a rotating condition,which made the anode in a state with alternating high and low current density.Electron probe micro analysis,ultra-depth microscope,scanning electron microscope,and X-ray photoelectron spectrometer were used to reveal the evolution of TA15 under fluctuating current density.The existence state of the passivation film on TA15 surface was closely related to the pulse frequency of the periodically fluctuating current density.At higher pulse frequency of 0.20 Hz,the material was hardly dissolved because passivation dominated the electrolysis behavior,while at lower pulse frequency of 0.01 Hz,the passivation and dissolution behaviors occurred alternately with the variation of the current density.Herein,the thickness of the passivation film was inversely proportional to the applied current density.Due to the different electrochemical characteristics of a phase andβphase,the surface of the TA15 changed from being smooth to porous after a period.In addition,the change of microstructure affected the content of O^(2–)and exposed the suboxides of titanium.In a word,the change of pulse frequency and current density affected the electrochemical behavior of TA15,which was different from the conventional steady condition.

Recent Advances in Near-Infrared Absorption Nanomaterials as Photoacoustic Contrast Agents for Biomedical Imaging

Photoacoustic imaging(PAI)is an emerging whole-body imaging modality offering high spatial resolution,deep penetration and high contrast in vivo.Signals for PAI are generated from contrast agents,where the laser-gen-erated optical energy is transferred to acoustic emissions and detected by an ultrasound transducer.A great deal of research over the past ten years has shown that near-infrared absorption nanomaterials such as organic dye-based nanoparticals,polymer-based nanoparticles,carbon-based nanomaterials and metallic nanomaterials are promising photoacoustic(PA)contrast agents,which can increase the imaging resolution,contrast and depth of detection.Hence,it is an attractive research field to develop new PA contrast agents.Herein,we reviewed this rapidly grow-ing field and described the applications of nanomaterial-based PA contrast agents for biomedical imaging.Particu-lar focus was given to organic near-infrared absorbing dyes including cyanine,porphyrin and boron-dipyrromethene derivatives.