GB∕T 28596-2012 内壁碳涂层聚对苯二甲酸乙二醇酯瓶

GB∕T 29403-2012 反击式水轮机泥沙磨损技术导则

The overall goal of this procedure is to achieve the highest possible resolution imaging in liquid, with a commercial AFM operated and amplitude-modulation, also known as tapping mode. This method helps pushing the limit of standard AFM operation in liquid, by using the best combination of parameters for high resolution. The main advantage of this technique is that it can be used with most commercial AFM's, and as such it doesn't require any specialist equipment. The method presented here is aimed at scientists and technician who already have some basic knowledge of AFM, but would like to get more out of the technique. This method is not aimed at any particular type of sample, and can be broadly applied to samples from physics, biology, chemistry, materials, and service sciences. Generally, individuals new to this technique will struggle, because it requires some patience to find the best parameters for a given sample. Bath sonicate the instruments, and the disk supporting the substrate in ultra pure water. Followed by isopropanol, and again ultra pure water, each for 10 minutes. When aiming for high resolution, any contamination can have detrimental consequences. Wear gloves at all times, and ensure that any surfaces or instruments that come in contact with the sample, cantilever, or AFM cell, are thoroughly cleaned. After sonication, dry each of the instruments and the sample disk under a flow of nitrogen. Use a steel disk as the support for mica, to image single absorbed metal ions. Physically clean the surfaces that can't be cleaned by sonication by wiping them with single ply low lint tissues soaked in ultra pure water, isopropanol, and ultra pure water sequentially. Allow the surface to dry in air for up to 30 minutes. Next, prepare a small amount of epoxy glue by thoroughly mixing the reagents, and place about 10 microliters of the epoxy on the clean steel sample disk. Place the mica substrate on the epoxy, and affix it to the steel disk by applying pressure on the substrate. Allow the epoxy to cure for several hours at an elevated temperature according to the manufacturer specifications. Then, firmly press a 2.5 centimeter wide piece of adhesive tape onto the substrate, so that the entire face is covered, and smoothly peel off the top layer. Repeat this process two to three times until the mica is mirror smooth to the eye. Immerse the cantilever chip in a bath of isapropanol followed by ultra pure water each for 60 minutes. Then, expose the tip to UV light for up to five minutes in order to favor the formation of stable hydration sites. Longer over-exposure times can damage the tip, or increase its radius of curvature. Insert the cantilever into the AFM's cantilever holder, and pipette 25 microliters of the imaging liquid onto the cantilever and tip to pre wet the surface. This will reduce the appearance of air bubbles when approaching the sample. Melt the sample disk and substrate onto the sample stage and add a droplet of the imaging liquid to the sample. Then connect the cantilever holder to the AFM. Bring the cantilever and sample into close proximity so as to form a capillary bridge between the fluids on the cantilever tip and those on the sample. Use the AFM software to align the measuring laser close to the tip end of the cantilever. Next, find the residence frequency of the cantilever from the main peak in its thermal spectrum. If the deflection of the cantilever is calibrated, fitting the residence peak with a simple harmonic oscillator model yields the spring constant of the cantilever. Then, tune the cantilever by finding its amplitude response when externally driven over a range of frequencies close to the resonance frequency identified in the thermal spectrum. Adjust the driving amplitude so that the free oscillation amplitude is approximately five nanometers. This typically corresponds with 0.2-0.8 volts on most AFM's. Then, adjust the amplitude set point to about 80%of the free amplitude. Next, set the feedback gains relatively high. After ensuring that no instability or ringing occurs, set the initial scan rate to about one hertz, and the scan size to 10 nanometers. Initiate the tip's approach to the surface using the AFM control software. Assess wether the tip has reached the surface without starting to image by slightly changing the set point value. If the tip is at the surface, the effect on the extension of the ZPA zone should be negligible. Once the tip has reached the surface, retract the ZPA zone and retune the cantilever. The resonance frequency will likely have shifted to a lower value due to tip sample interactions. Now, change the set point to about 80%of the newly tuned free amplitude, and engage the cantilever to conduct a 10 by 10 nanometer squared scan of the surface in amplitude modulation mode to verify that the imaging parameters are suitable. Check that the trace and retrace profiles superimpose. If not, further reduce the set point, and try increasing the gains. If the image becomes noisy, lower the gains. Repeat the operation with a large one to five micrometer squared region of the sample, provided this is possible. On soft or biological samples, this might result in contamination of the tip. Reduce the scan size to a value suitable for visualizing the features of interest. This can be as low as 20 by 20 nanometers. Next, reduce the drive amplitude of the cantilever enough for the feedback loop to automatically retract the ZPA zone, enhance the tip from the surface. While the cantilever is away from the surface, adjust the drive amplitude so that the cantilever amplitude is one to two nanometers peak to peak. Progressively reduce the set point in small steps, until the ZPA zone extends again towards the surface, and the original image is recovered. Keep the set point amplitude between 75%and 95%of the new free amplitude. Then, readjust the gains, since higher gains can be used at lower amplitudes without introducing significant noise. Optimize the system to find the best combination of free amplitude, set point, and gain for high resolution. The optimum system conditions depend on the sample, the wetting properties of the liquid, and also the cantilever being used. For solvophilic interfaces, use cantilevers with a spring constant of 0.5 to two newtons per meter. Using this technique, sub nanometer resolution images were obtained over a broad range of samples. The soft samples shown here include a lipid bilayer, purple membranes from halobacterium salinarum, a self assembled monolayer of amphophilic dimolecules, and aquaporin crystals from a bovine lens membrane. In each case, the features of interest are highlighted. The small oscillation amplitudes and high set points minimize the force exerted by the tip on the sample, allowing for the fragile self assemblies of lipids in the bilayer, proteins in native biomembranes, and amphophilic molecules to be imaged in solution without damage. Harder crystalline materials, such as calcite, strontium titanite, silicon carbide, and single metal ions absorbed on a mica surface can be imaged using this approach, because in every case, it is the interfacial liquid that is effectively imaged, not the crystal itself. Once mastered, this technique provides molecular or atomic level resolution in liquid almost every time it's performed correctly. When attempting this procedure, it's important to bare in mind that it's the interfacial liquid being imaged. This means using soft imaging conditions. Contamination of the tip, the sample, or the liquid is usually the main cause for failing to achieve high resolution. If in any doubt, it is often a good idea to clean all the surfaces in contact with the liquid, and reuse imaging solutions. External noise is also detrimental to high resolution. A low vibration floor, away from a ventilation duct is better. After watching this video, you should have a good understanding of how to optimize your imaging parameters to achieve high resolution AFM. Of course, as for any cutting-edge technique, it can take several trials to figure out how to best image a sample, so patience is key.

The goal of this protocol is to produce two dimensional nanosheets stabalized in liquid with controlled lateral size and thickness from bulk crystals. We also demonstrate methods to characterize the morphology and quantitatively determine the nanosheet dimensions from extinction spectra. This method can help answer key questions in nanoscience, such as the influence of nanosheet dimensions on the properties of structures and composites containing these sheets exfoliated in liquid. The main advantage of this technique is that it's applicable to many different true day materials and only requires commonplace laboratory equipment. In particular, the spectroscopic metrics allow rapid assessment of the dispersions that are produced. Demonstrating the procedure will be Farnia Rashvand, a PhD student, and Kevin Synnatschke, a Master's student from my laboratory. To begin this procedure, mount a metal cup underneath a sonotrode in an ice bath. Immerse 0.6 grams of a transition metal dichalcogenide or TMD powder in 80 milliliters of an aqueous solution of sodium cholate surfactant in the metal cup. Move the solid flathead tip to the bottom of the metal cup and then raise it approximately one centimeter. Wrap aluminum foil around the sonic probe to avoid spillage. To sonicate the mixture by probe sonication, set the amplitude to 60%and the pulsing to six seconds on, and two seconds off. Then switch on the sonicator and run the process for one hour. Next, centrifuge the dispersion at 2, 660 times g for 1.5 hours. After discarding the supernatant, add 80 milliliters of fresh surfactant solution to the sediment and agitate the mixture. Then, transfer the mixture back to the metal cup. Now, subject the dispersion to a second, longer sonication using the solid flathead tip for five hours at 60%amplitude under ice cooling. After every two hours, pause the sonication and replace the ice bath. Remove unexfoliated particles by centrifugation at 240 times g for two hours. When finished, discard the sediment. Following this, centrifuge the supernatant at higher centrifugal acceleration. Collect the sediment in three to eight millileters of fresh surfactant solution. Centrifuge the supernatant at an even higher centrifugal acceleration of 950 times g for two hours. Then collect the sediment in three to eight milliliters of fresh surfactant solution. For atomic force microscopy, dilute the dispersion so that it is almost transparent to the human eye. Following this, heat a wafer to approximately 170 degrees Celsius on a hot plate. Then deposit the dispersion on the preheated wafer. Rinse the wafer thoroughly with a minimum of five milliliters of water and three milliliters of 2-Propanol to remove residual surfactant and other impurities. Following this, load the sample in AFM instrument. Scan and save multiple images across the sample with the atomic force microscope in tapping mode. For samples containing larger nanosheets, increase the field of view up to eight by eight micrometers squared and use scan rates of 0.4 to 0.7 hertz. To perform the thickness measurement, open the software and select the relevant AFM image via File and Open. Correct the background using the level data by mean plane subtraction, align rows, and correct horizontal scars in the data process of the Home menu. Apply the corrections, change the image color for better contrast by right-clicking on the the legend and set the Z plane to zero. Next, zoom into the region of choice by first clicking on the Crop tool in the Home menu. Then drag the cursor over the image to mark the region of choice and press Apply. Check the create new channel to open the selected region in a new window. Select extract profiles from the Tools menu and draw a line across the nanosheet. After the window showing the thickness length profile opens, enter the thickness value in a table. Take the approximate median value of the thickness profile across the nanosheet, taking extreme care to measure only individually deposited and non-aggregated nanosheets. For spectral acquisition, dilute the high concentration sample with the respective medium to yield extinctions below two across the entire spectral range. Set the increments for spectral acquisition to 0.5 nanometers in the instruments setting. Choose subtract baseline in the instruments settings. After placing a cuvette containing the aqueous sodium cholate solution in the spectrometer, run the measurement. Following this, remove the cuvette from the spectrometer and empty it. Add the sample to the cuvette and place the cuvette in the spectrometer. Then run the measurement. Using the data analysis and graphing software, select the column containing the extinction intensity. Click on the Analysis tab, select Mathematics from the dropdown menu, and click on Differentiate. Then select Open Dialog. After the new window opens, set the derivative order to two and press OK.Select the column containing the derivative, click on Analysis and choose Signal Processing. Click on Smooth and then select Open Dialog from the dropdown menu. Next, choose Adjacent Averaging as the smoothing method and set the points to 20. Plot the resultant smoothed spectrum, which is displayed as new columns. Finally, read off the peak position from the second derivative by placing the cursor in the center of the peak. Liquid cascade centrifugation is used to sort liquid-exfoliated nanosheets by size and thickness as demonstrated for molybdenum and tungsten disulfide. A typical AFM image is shown here. And the nanosheet thickness is converted to layer number using step height analysis. Statistical microscopic analysis yields length and number of layer histograms. The mean nanosheet length and layer number plotted as a function of central acceleration shows a similar trend for both materials. The length plotted as a function of nanosheet layer number confirms that smaller, thinner nanosheets are separated from larger, thicker ones. Optical extinction spectra of molybdenum and tungsten disulfide with different mean nanosheet sizes and thicknesses are shown here. The corresponding fitted second derivatives of the A-exciton region illustrate well-defined peak shifts of the transition. Data for both materials collapses on the same curve if appropriate peak positions are chosen and means that the nanosheet size can be quantitatively linked to the nanosheet length via the same equations. The A-exciton extinction coefficient is length dependent except at certain positions, so that the corresponding extinction coefficient can be used as measure for nanosheet concentration. The number of layers can be quantitatively related to the A-exciton peak position. Once mastered, large quantities of liquid-exfoliated nanosheet dispersions with controlled and known dimensions can be produced in only a couple of days. This is enabled by the high throughput size determination based on the optical extinction spectra. Since the nanosheet size determines its properties, the size control is crucial. After the development of the metrics, this technique paved the way for researchers to explore them in a number of applications, from electrocatalysis to electronics to composite reinforcement. After watching this video, you should have a good understanding of how to produce size selected nanosheet dispersions using liquid phase exfoliation and liquid cascade centrifugation procedures. Following the dispersion preparation, it's very important to perform basic characterization using statistical microscopy and optical extinction spectroscopy to confirm the nature of the dispersion constituents. Most excitingly, the resulting size selected nanosheet dispersions can then be subject to various liquid phase processing methods to produce thin films and other nanosheet containing structures for a wide range of potential applications.

本书以24.5吋车用盘式制动器为研究对象，系统阐述制动系参数选择及制动器的设计计算，开发了制动器参数化设计系统；开展24.5吋盘式制动器结构强度试验研究，完成关键零部件强度的有限元分析和结构优化；开展24.5吋盘式制动器的热机耦合试验研究，完成紧急制动工况和连续制动工况下制动器温度场、应力场分析；开展制动器摩擦材料分析及试验研究，揭示盘式制动器摩擦磨损机理；介绍制动器性能检测技术，研制制动器总成疲劳试验台。