近壁面超声空化微射流对微细颗粒的破碎作用

针对微细粉体“团聚”导致粉磨极限的问题,在液相环境下利用超声的分散和空化冲击作用,开展了近壁面超声空化微射流对微细颗粒破碎作用的研究。通过理论计算空化微射流冲击微细颗粒破碎的有效作用范围,从空化泡溃灭速度的角度分析了超声频率、声压幅值、介质尺寸等主要参数对微射流强度的影响;结合物料质量浓度、介质尺寸、介质面积和功率等影响因素的微细颗粒超声空化破碎正交试验,并利用SEM观测粉体形貌,分析了颗粒中位粒径D 50、10%体积累积粒径D 10和比表面积(SSA)等分布特性。参数组合优化后获得了粒径小于800目的微细颗粒,破碎率高达79.35%;粒径大于10000目的极细颗粒产率高达12.84%。从提高微细颗粒破碎率的角度,发现介质面积是主要影响因素,功率次之,其次为介质尺寸和物料质量浓度。试验结果与理论研究成果基本一致,表明优化超声空化微射流参数与增加介质壁面面积等方法可有效提高微细颗粒的破碎率。

Effects of solution treatment on mechanical properties and microstructures of Al-Li-Cu-Mg-Ag alloy

Mechanical properties and microstructures of Al-Li-Cu-Mg-Ag alloy after solution treatments were investigated by means of optical microscopy （OM）, tensile test, hardness measurement and electrical conductivity test, differential scanning calorimetric （DSC）, energy dispersive X-ray （EDX）, scanning electron microscopy （SEM） and transition electron microscopy （TEM）, respectively The results show that both tensile strength and hardness increase first and then decrease with temperature at constant holding time of 30 min with maximum strength and hardness appearing at 520 ℃. Tensile strength, hardness and elongation of samples treated at 520 ℃ for 30 min are 566 MPa （σb）, 512 MPa （σ0.2）, HB 148 and 8.23% （δ）, respectively. There are certain amount of fine T1 （AI2CuLi） phase dispersing among AI substrates according to TEM images. This may result in mixed fracture morphology with trans-granular and inter-granular delamination cracks observed in SEM images.

Retrieving analog images from a scanning electron microscopewith a synchronous data acquisition method

In this work,an old scanning electron microscope(SEM)is refurbished to enhance its image processing capability.How to digitally sample and process an analog image is also presented.An NI PCI-6259 multiple input/output data acquisition(DAQ)board is used to acquire signals originally being sent to an analog display,and then convert the signals into a digital image.Two output channels are used for raster scan of the horizontal and verticle axes of the image buffer,while one input channel is used to read the brightness signals at various coordinate points.Synchronous method is used to maximize the DAQ speed.Finally,the digitally buffered images are read out to display and saved in a hard drive.The hardware and software designs of this work are explained in great detail,which can serve as a very good example for fast synchronous DAQ,advanced virtual instrument design and structural driver programming with LabVIEW.

Preparation and infrared emissivities of alkali metal doped ZnO powders

Alkali metal(Li, Na, K) doped ZnO powders were synthesized by solid-state reaction at different calcination temperatures and holding time. Effects of holding time and K sources on the infrared emissivity of ZnO were investigated. The structure and surface morphologies of samples were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM). The UV-Vis absorption and infrared emissivities were investigated by a UV-Vis spectrophotometer and an infrared emissometer, respectively. XRD patterns confirm the wurtzite structure of the as prepared samples with single phase. Smooth grain surfaces are detected in all doped ZnO samples, while ZnO:Li and ZnO:Na present the aggregation of grains. The redshifts in the optical band-gap are observed in K-, Na-, and Li-doped ZnO with the values 3.150, 3.144, and 3.142 eV. Due to better crystalline quality, ZnO:K shows a lower emissivity than others. The emissivity of K-doped ZnO decreases to the minimum value(0.804), at 1200 °C and holding 2 h. Compared with KNO3 as K source, K2CO3 doped ZnO has lower emissivities.

Removal of reactive bright-red X-3B in water by Ti/13X molecular sieves

The compound materials （shorted by Ti/13X） of doping of TiO2 into 13X molecular sieves has-been achieved by methods namely impregnation. Technical parameters of preparation for Ti/13X were determined by removal efficiency of simulation dyeing wastewater containing reactive bright-red X-3B （shorted by X-3B）. In various preparation parameters, the influence of Ti loaded on 13X molecular sieves on X-3B removal efficiency is most important. The optimum condition for volume of TiCI4 loaded on 13X molecular sieves is 8 ml at 95.9%, produced sample referred as M8. M8 was characterized using X-Ray Diffraction （XRD）, Scanning Electron Microscope （SEM）. XRD patterns of M8 revealed the incorporation of titanium into framework of 13X molecular sieves, due to the presence ofTiO2 anatase phase. SEM image showed that M8 has a large number of wormhole-like channels, in comparison with that of 13X molecular sieves. The photocatalytic tests were carried out for degradation of X-3B. The results showed that the dosage of Ti/13X, reaction time, pH, and concentration of X-3B influence the X-3B removal efficiency. The optimum conditions of photodegradation as the following： MS/X-3B ratio, Conc. is 0.3 g/l, reaction time is 120 rain, pH is 2-6. The photodegradation reaction of Ti/13X with X-3B followed first order kinetics. The rate constants and t1/2 for M8 sample at 0.3 g/l M8/ X-3B solution ratio were 430 min^-1 and 16 min, respectively.

Droplet Contact Angle Measurement on Microstructures of Octocoral Sclerites-ESEM Image Analysis

This work explores the methodology for micron-scale water droplet contact angle derivation for the warty surface of octocoral sclerites. The calcite-made sclerites of the Red Sea octocoral Dendronephthya hemprichi have been chosen as a model for this study. Water droplet condensation on the sclerites has been in-situ investigated using Quanta 200 FEG （field emission gun） ESEM （environmental scanning electron microscope） under wet environmental conditions. Two different analysis methods of droplet top and side views have been applied to determine the contact angle based on the secondary electron images. The ESEM image analysis for the sclerites indicates that their surface is hydrophilic. The microscopic contact angle is measured to be 45.3°±6.3°. The macroscopic contact angle has been calculated by using the Wenzel model for the surface texturing of the sclerites.

Fabrication technique of micro/nano-scale speckle patterns with focused ion beam

The fabrication technique of micro/nano-scale speckle patterns with focused ion beam (FIB) system is studied for digital image correlation (DIC) measurement under a scanning electron microscope (SEM).The speckle patterns are fabricated by directly etching the counterpart of the specimen to the black part of a template.Mean intensity gradient is used to evaluate the quality of these SEM images of speckle patterns fabricated based on different templates to select an optimum template.The pattern size depending on the displacement measurement sensitivity is adjusted by altering the magnification of FIB according to the relation curve of the etching size versus magnification.The influencing factors including etching time and ion beam current are discussed.Rigid body translation tests and rotation tests are carried out under SEM to verify the reliability of the fabricated speckle patterns.The calculated values are in good agreement with the imposed ones.

Applications of scanning electron microscopy in earth sciences

This paper expounds upon the basic principle of scanning electron microscopy(SEM),the main features of image types,and different signals,and the applications and prospects in earth sciences research are reviewed.High-resolution field emission SEM allows observation and investigation of a very fine micro area in situ.Using low-vacuum mode SEM,geological insulating samples can be analyzed directly without coating,demonstrating the wide application prospect.Combined with backscatter detector(BSE),energy dispersal X-ray spectroscopy(EDS),cathodoluminescence spectrometry(CL),and electron back-scattering diffraction(EBSD),SEM can yield multiple types of information about geological samples at the same time,such as superficial microstructure,CL analysis,BSE image,component analysis,and crystal structure features.In this paper,we use examples to discuss the geological application of SEM.We stress that we should not only focus on the CL image analysis,but strengthen CL spectrum analyses of minerals.These results will effectively reveal the mineral crystal lattice defects and trace element composition and can help to reconstruct mineral growth conditions precisely.