中性变密度盘的加工与检测

本文就加工－精度要求高，且口径厚度比为３５：１的薄形零件，设计了多种加工及上下盘方法，并用激光平面干涉仪测试加工过程，从而加工出高质量的零件．     

纯物质自由枝晶生长特征的Fourier变换研究

本文用光学中Fourier变换的概念和方法处理纯物质自由枝晶尖端前沿的热势波传输问题,进而描述其凝固界面生长形态变化特征。具体做法是:先将热势波与枝晶端部作用后的传播过程用Fourier变换表示出来,从而求得了热势的空间分布,再由热势的分布特征反推出枝晶尖端界面生长形态的演化特点。这种方法还可简洁地处理界面能各向异性对界面凝固生长特征的作用问题。     

Mild ketone formation via Ni-catalyzed reductive coupling of unactivated alkyl halides with acid anhydrides

Ni-catalyzed ketone formation through mild reductive coupling of a diverse set of unactivated alkyl bromides and iodides with particularly aryl acid anhydrides was successfully developed using zinc as the terminal reductant. These conditions also allow direct coupling of alkyl iodides with aryl acids in the presence of Boc(2)O and MgCl(2).     

Preparation and Characterization of Melamine-Formaldehyde Resin Micro- and Nanocapsules Filled with n-Dodecane

Capsules containing phase change materials (PCMs) have been widely studied for applications in heat transfer, heat storage and temperature control. The average diameter of encapsulated PCMs usually has a large effect on the physical properties of these functional materials. The aim of this study was to prepare and characterize encapsulated n-dodecane, a kind of PCM with a phase change temperature at about ?10°C, in micro- and nanoscales via an in-situ polymerization method with melamine-formaldehyde resin (MF) as the shell. By analyses with scanning electronic microscopy, Fourier transform infrared spectroscopy and ¹³C nuclear magnetic resonance, it was found that the obtained capsules containing n-dodecane were on microns or several hundreds of nanometers size with spherical shape and smooth surface, and the agglomeration of the capsules was mainly dependent on the average diameters which was controlled by the stirring rate during emulsification of n-dodecane, as well as the concentration of the emulsifying agent and the reaction temperature. Thermogravimetric analysis showed that the n-dodecane capsules increased their thermal stability with decreased diameter. The results of differential scanning calorimetry showed that the supercooling degree of n-dodecane in nanocapsules was somewhat higher than that in the microcapsules, and the suppression of supercooling is considered.     

Influence of initial solid–liquid interface morphology on further microstructure evolution during directional solidification

Preparation of the initial solid–liquid interface on which growth is started is a very critical step in directional solidification experiments. Dedicated experiments concerning preparation of the initial solid–liquid interface morphology and its influence on further directionally solidified microstructure were performed on Cu-20 wt% Sn peritectic alloy in a Bridgman-type furnace. To verify the morphology of the initial solid–liquid interface, steady-state directional dendritic growth was interrupted by thermal stabilization ranging from 0 to 1 h prior to quenching. With thermal stabilization duration increase, the solid–liquid interface morphology degenerated from dendritic to cellular and finally to planar. To verify the influence of the initial state on further solidification microstructure, directional solidification experiments were performed at a low pulling rate of 1 μm/s with different initial solid–liquid interface morphologies. The initial state affects solute redistribution and formation of peritectic coupled growth structure in the subsequent directional solidification process.     

Microstructure and field emission properties of the Si–TaSi2 eutectic in situ composites by electron beam floating zone melting technique

The directionally solidified Si–TaSi₂ eutectic in situ composites, which have highly aligned and uniformly distributed TaSi₂ fibers embedded in the Si continuous matrix, are obtained by electron beam floating zone melting (EBFZM) technique at the solidification rate range 0.3–9.0 mm/min. The preferential orientation of the Si–TaSi₂ eutectic is also studied by selected area electron diffraction (SAED), which is [0 1¯ 1¯]Si∥[0 0 0 1]TaSi₂ and (0 1¯ 1)Si∥(0 1¯ 1 1)TaSi₂. Moreover, field emission properties of the Si–TaSi₂ eutectic in situ composites are investigated by transparent anode imaging technology. Approximately straight F–N curves show that this material has excellent field emission properties.     

定向凝固界面速率对机械牵引速率的响应

通过传热分析,给出了定向凝固过程中界面速率对机械牵引速率的响应函数,指出在低速凝固条件下,界面速率可以视为与牵引速率相等;而在高速凝固时界面速率相对于牵引速率存在滞后现象.两个速率保持同步的上限值受到冷却环境、试样尺寸、合金热物理性质等的影响.液相前沿的温度梯度与冷却介质、加热方式以及合金体系有关.在此基础上,分析了实现稳定的亚快速定向凝固的条件.     

不确定度在工科基础物理实验中的应用举例

本文扼要地介绍测量不确定度的定义及计算方法,并针对大学低年级工科基础物理实验的要求,列举了在基本测量实验中求铜管体积的具体应用,希望学生淡化误差,养成不确定度应用于数据处理中的良好习惯。