一种快速的自由曲面三轴数控加工干涉检查方法

通过深入研究提出了一种直线段相对于圆形窗口位置关系的快速判别方法 ,以此方法可以大大提高分析逼近曲面的三角片与刀具在刀轴方向的投影之间关系的效率 ,从而加快了自由曲面三轴数控加工的干涉检验速度     

Observation and analysis of epitaxial growth with reflectance-difference spectroscopy

Reflectance-difference (RD) (-anisotropy) spectroscopy has developed into an established diagnostic tool for semiconductor epitaxy. Major advantages include the simplicity of the approach and the capability of performing measurements in real time during growth. Studies to date have emphasized understanding the origin of RD spectra, relating them to electronic and atomic structure of growth surfaces, and using them to obtain information about fundamental mechanisms of epitaxy. The observation of RD oscillations during organometallic chemical vapor deposition, oscillations that are analogous to those seen in reflection high energy electron diffraction intensities during molecular beam epitaxy, is providing new opportunities for growth control. Using (001) GaAs as an example, principles, representative results, and current critical issues are discussed.     

癸烷在二氧化硅表面的油膜形成与表面润湿性

用二氧化硅片作为模拟岩石，以椭圆偏振法测量癸烷在其表面形成的油膜厚度，通过长度测量法测定水在二氧化硅表面的接触角来判断润湿性及润湿性的变化。亲水的二氧化硅表面难以形成油膜，而疏水的二氧化硅表面能形成较厚而稳定的油膜。疏水或近中性的二氧化硅表面在经碱水作用或吸附表面活性剂后，在特定的条件下能变成弱亲水或亲水，从而将油膜破坏。     

Surface modification of zinc oxide nanoparticles by aminopropyltriethoxysilane

Commercial zinc oxide nanoparticles (20–30 nm) were coated by aminopropyltriethoxysilane (APTES) under varying environments. Three different processes, acidic, basic and toluene were used. The effects of coating conditions (acidic, basic and toluene) on the grafting, structural and optical properties of these nanoparticles were studied. In the three cases, it was possible to control the coating and according to X-ray diffraction, BET, TEM and SEM results, it is clear that the APTES coating plays a role of growth inhibitor even at 800 °C. From diffuse reflectance measurements, one can notice that the grafting process did not modify the transmittance spectra of ZnO.     

Nucleate boiling heat transfer coefficients of HFO1234yf on various enhanced surfaces

In this study, nucleate boiling heat transfer coefficients (HTCs) of HFO1234yf HFC134a are measured on a flat plain, Turbo-B, Turbo-C, and Thermoexcel-E surfaces. All data are taken at the liquid pool temperature of 7 °C on small flat horizontal square copper plates (9.53 mm × 9.53 mm) at heat fluxes from 10 kW m⁻² to 200 kW m⁻² with an interval of 10 kW m⁻². Test results show that nucleate boiling HTCs of HFO1234yf on all four surfaces are similar to those of HFC134a at all heat fluxes tested in this study. At heat fluxes below 150 kW m⁻², Thermoexcel-E surface shows the highest heat transfer performance and hence is the best surface for the manufacture of the evaporators in refrigeration and air-conditioning equipment. On the other hand, at high heat fluxes above 150 kW m⁻², Turbo-B and Turbo-C show better heat transfer performance than Thermoexcel-E and hence are good for electronic cooling applications. Overall, HFO1234yf is a good long term candidate with excellent environmental properties to replace successfully HFC134a from the view point of pool boiling heat transfer. Hence HFO1234yf can be readily applied to the conventional evaporators designed for HFC134a.     

Structural,spectroscopic and biological investigation of copper oxides nanoparticles with various capping agents

Powder composed of copper oxides nanoparticles with various capping agents has been synthesized and characterized with the use of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Polyvinyl alcohol (PVA), glycol propylene, glycerin and glycerin plus ammonia were used as capping agents. The scanning electron microscopy (SEM) studies showed that nanoparticles form agglomerates with the size from 80 to 120 nm while particles size determined from the XRD experiment was in the range from 7 to 21 nm. XPS and XRD experiments revealed that depending on capping and reducing agents used in the synthesis nanoparticles are composed of Cu₂O, CuO or a mixture of them. The biological activity test performed for a selected sample where the capping agent was glycerin plus ammonia has shown promising killing/inhibiting behavior, very effective especially for Gram negatives bacteria.     

Improving conversion efficiency of CdS quantum dots-sensitized TiO2 nanotube arrays by doping with Zn and decorating with ZnO nanoparticles

The Zn-doped TiO₂ nanotube arrays (TNTs) decorated with ZnO nanoparticles have been prepared via electrochemical anodization and immersing method. Furthermore, the CdS quantum dots (QDs) were deposited on the prepared Zn-doped TNTs-ZnO thin films by chemical bath deposition (CBD) method to fabricate the CdS QDs-sensitized Zn-doped TNTs-ZnO photoelectrodes. The nanostructure, morphology, optical properties and electrochemical properties of the CdS/Zn-doped TNTs-ZnO photoelectrode with comparison to those of the CdS/TNTs photoelectrodes were investigated. It has been found that the Zn-doped TNTs-ZnO photoelectrodes significantly increased the UV–vis light absorption of the CdS/Zn-doped TNTs-ZnO photoelectrodes and reduced the charge recombination at the surfaces of the CdS/Zn-doped TNTs-ZnO photoelectrodes. As a consequence, when the Zn-doped TNTs-ZnO film was adopted instead of the plain TNTs film, the light-chemical energy conversion efficiency of the CdS/Zn-doped TNTs-ZnO photoelectrode was much improved compared with the CdS/TNTs photoelectrode. A maximum energy conversion efficiency achieved for the CdS/Zn-doped TNTs-ZnO photoelectrode is 3.86%, which is a 17% improvement compared with the maximum energy conversion efficiency of 3.29% achieved for the CdS/TNTs photoelectrodes.     

ZnO films grown on cotton fibers surface at low temperature by a simple two-step process

Zinc oxide (ZnO) films have been synthesized and deposited onto cotton fiber surface using a simple two-step process. At first step, the cotton fiber surface was coated with a conductive layer of zinc-cellulose complex by rinsing the fibers in zinc chloride solution. After that, the growth of ZnO films was carried out in zinc acetate aqueous solution at room temperature, with alkaline aqueous solution drops continuously added under magnetic stirring. The morphology of the as-prepared ZnO-coated cotton fibers was characterized by scanning electron microscopy. Infrared and photoluminescence spectra were used to confirm the existence of ZnO. In addition, the formation mechanism of ZnO-coated cotton fibers is discussed in detail.     

Effect of zirconia sol in electrolyte on the characteristics of microarc oxidation coating on AZ91D magnesium

The microarc oxidation coatings were prepared on AZ91D magnesium alloy in a Na₂SiO₃-KOH electrolyte with and without zirconia sol, respectively. The effect of zirconia sol as an additive in the electrolyte on the surface morphologies, compositions, structures, and corrosion resistances of the coatings were investigated. It was found that the coating formed in the Na₂SiO₃-KOH electrolyte with zirconia sol has more uniform morphology, less micropores and cracks than that formed in an electrolyte without zirconia sol. The phase compositions of the coatings also varied after addition of zirconia sol in the electrolyte, owing to the participation of zirconia sol in the reaction and its incorporation into the oxide coating, and Zr existed in the form of Mg₂Zr₅O₁₂. The results of potentiodynamic polarization analysis show that the coating formed in the electrolyte with zirconia sol increases significantly corrosion resistance for magnesium alloy.     

Carbon rich surface of LiFePO4 grain enhancing its rate capability

LiFePO₄/C composite with carbon content of 5 wt.% was synthesized by solid state reaction. Core-shell structure was confirmed by scanning electron microscope (SEM) and transmission electron microscopy (TEM). Rechargeable Lithium ion battery based on this compound has reached a high rate capacity of 121.5 mAhg^− 1 under 5 C. The rate capability retention between 0.1 C and 5 C is 86.9%, which is the highest as far as we know. We found the carbon content was 12.7% on the surface of LiFePO₄ grain, although the whole carbon content was about 5 wt.%. We attribute the improvement of rate capability retention to the existence of the carbon rich surface.