Sonochemical synthesis of ZnO‐ZnS core‐shell nanorods for enhanced photoelectrochemical water oxidation

The ultrasonic‐assisted synthesis method provides a fast, simple, and large‐scale route for synthesizing desired materials under ambient conditions. In this work, we report on the facile preparation of ZnO‐ZnS core‐shell nanorods on a fluorine‐doped tin oxide (FTO) substrate. The core‐shell nanorods were synthesized by sequential nanoscale reactions involving the preparation of ZnO nanorods and conversion of the ZnO surface into a ZnS shell on the FTO substrate, using an in situ sonochemical method. The ZnO‐ZnS core‐shell nanorods showed improved photocurrents compared with ZnO nanorods for the water oxidation reaction. During the water oxidation reaction, the ZnS shell passivates the surface‐defects of the ZnO, which results in enhanced charge separation in the ZnO nanorods and higher performance.     

Ultrasonic characterization of residual stresses in steel rods using a laser line source and piezoelectric transducers

The surface residual stresses in steel rods made of the same material but with different heat treatments have been studied from Rayleigh wave velocity measurements using the laser ultrasonics technique and piezoelectric transducers. The Rayleigh wave velocities, both along the circumference and in the axis direction on the cylindrical surface of every rod, are measured and compared with one another in order to evaluate qualitatively the surface stress state for each rod. The experimental results clearly show that the Rayleigh wave velocities on the cylindrical surfaces of these rods are different, and the results obtained by laser ultrasound are in good agreement with those measured with piezoelectric transducers. From the measured velocities, different stress states have been identified for these rods according to the heat treatments they have undergone.     

Nanoparticle removal from trenches and pinholes with pulsed-laser induced plasma and shock waves

Removing nanometer scale particles from patterned substrates is a critical, yet challenging, technical task with numerous applications. Due to environmental concerns, there is a drive to reduce chemical usage and waste in semiconductor and other nano-technology industries. The laser plasma method is a novel removal method for nanoparticles. For the work reported in this study, the method is applied to substrates with features, i.e. trenches and pinholes. The technique, which is dry and non-contact, takes advantage of shock wavefronts initiated by plasma formation under a focused laser beam pulse and their interaction with the substrate. In the reported experiments, a Q-switched Nd : YAG pulsed laser is employed as a plasma and shockwave generation source. Various mechanisms are responsible for the removal effect. The strong shock wave in air generates complex pressure wavefields resulting in both drag and lift on the particle and acceleration of the substrate. However, shock waves are not transmitted into the solid substrate as discontinuous shock fronts due to a large difference between the relevant wave phase speeds in the two media. Also, damage concerns due to cavitation, which is a common effect in megasonic cleaning, are avoided. However, damage due to the high temperatures associated with the plasma formation is found to be an issue. Patterned silicon wafers and micrometer level pinholes were used for the particle removal experiments. The effects of the distance between the surface and the plasma boundary on the removal efficiency are reported. With this method, we were able to remove particles from the wall of a micrometer level pinhole and patterned silicon wafers.     

Preliminary experiments in acoustoelastic responses of a plastically deformed solid

Abstract

In this paper, the details of the experimental techniques and set‐ups needed in the acoustic birefringence measurement are given. To precisely determine the wave speeds, the Echo‐Overlap method with reflection mode is adopted. The details of the fabrication of a dual‐polarization ultrasonic shear‐wave transducer are also included. The anelastic effect which occurs in the acoustoelastic measurement of a plastically deformed steel (C1018) specimen is examined. The general assumption of slight orthotropy which is used in ultrasonic stress measurement of polycrystalline metal is tested. The annealing experiment shows that the preferred orientation of the cold‐rolled steel plate can not be changed by annealing the specimen at the recovery temperature. The measurement of the third order elastic constants of the steel specimen is also conducted.     

Assessment of Sensitization in AISI 304 Stainless Steel by Nonlinear Ultrasonic Method

A nonlinear ultrasonic technique has been developed to evaluate sensitization in Type 304 stainless steel.In order to achieve diferent degree of sensitization(DOS),specimens have been subjected to heat treatment at 675℃ at varying soaking time(0.5,1.0,2.0,3.0 and 4.0 h).Heat treated specimens were subjected to intergranular corrosion tests as per ASTM standards A262 and G108.Sensitization in longer soaked material has been confirmed through ditch microstructures,cracks on the bend tested specimens and higher degree of sensitization.Nonlinear ultrasonic studies showed variation in the nonlinearity parameter with soaking time which also confirms sensitization.A good correlation was observed between the degree of sensitization measured by the electrochemical potentiokinetic reactivation test and the ultrasonic nonlinearity parameter.This study clearly demonstrated that nonlinear ultrasonic technique can be used as a potential technique for non-destructive characterization of sensitization in austenitic stainless steel.     

基于LabVIEW的激光超声测量虚拟仪器研究

给出了一种确定超声信号直达声时的方法,建立激光超声测量实验装置,研制了基于LabVIEW测量系统可视化虚拟仪器,用于材料物理参数的测量.实验结果表明,该系统操作简单,易实现,软件界面友好,可扩展性强;具有较高测量精度,测量材料厚度时,相对误差为2.51%,测量材料声速时,相对误差为2.57%.     

Miniaturized Lab-on-a-Disc (miniLOAD)

A miniaturized centrifugal microfluidic platform for lab-on-a-chip applications is presented. Unlike its macroscopic Lab-on-a-CD counterpart, the miniature Lab-on-a-Disc (miniLOAD) device does not require moving parts to drive rotation of the disc, is inexpensive, disposable, and significantly smaller, comprising a 10-mm-diameter SU-8 disc fabricated through two-step photolithography. The disc is driven to rotate using surface acoustic wave irradiation incident upon a fluid coupling layer from a pair of offset, opposing single-phase unidirectional transducers patterned on a lithium niobate substrate. The irradiation causes azimuthally oriented acoustic streaming with sufficient intensity to rotate the disc at several thousand revolutions per minute. In this first proof-of-concept, the capability of the miniLOAD platform to drive capillary-based valving and mixing in microfluidic structures on a disc similar to much larger Lab-on-a-CD devices is shown. In addition, the ability to concentrate aqueous particle suspensions at radial positions in a channel in the disc dependent on the particles' size is demonstrated. To the best of our knowledge, the miniLOAD concept is the first centrifugal microfluidic platform small enough to be self-contained in a handheld device.     

A self-tuning ultrasonic sensor based powder injection molding process

Ultrasonic sensors show great promise in defect detection and classification when monitoring the powder injection molding (PIM) manufacturing process. To date, however, these sensors are not used in a closed-loop control system. A simplex method is developed that automatically tunes a manufacturing system operating conditions on the basis of in situ ultrasonic sensor readings. Potential applications for this system include the initial set-up of optimal manufacturing conditions and also tracking of the optimum conditions in situ during long-term operation.     

Anisotropic character and ultrasonic stiffness changes during the natural weathering of LDPE films

Blown extruded polyethylene films without stabilizers have been exposed outdoors under severe weathering conditions in the Sahara. The chemical aspect of aging has been followed by IR spectroscopy. The mechanical aspect of aging has been monitored by means of a nondestructive method. It consists of measuring velocities and attenuations of ultrasonic waves propagating in several directions in the film plane. Stiffness constants and energy dissipation terms have been calculated. From the results obtained it is shown that stiffening of the material leads to an increase of velocities and a decrease of wave attenuation. Moreover, the stiffness constants as well as the energy dissipation terms vary with aging and show a changing anisotropic character of the films. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 559–564, 2003     

Influences on signal/noise ratio during ultrasonic inspection of composites

This paper investigates the correlation between transducer properties, defect size and depths, and the signal/noise ratio during ultrasonic inspection of polymeric composites. Samples of different fibre/matrix systems were produced, including artificial defects of various size and shape. These specimens were inspected ultrasonically with transducers in the frequency range from 1 to 150 MHz. It could be seen that the 5 MHz transducer possessed the highest signal/noise ratio in most cases. A transducer selection catalogue incorporating special usage terms for carbon fibre/epoxy resin composites is introduced.